kono sigoto wo sassato owaraseyou.

Because この is a demonstrative adjective, so it directly modifies the noun that follows it.

• この仕事 = this job / this work
• You do not say このの仕事

Compare:

• この仕事 = this job
• その仕事 = that job
• あの仕事 = that job over there

If これ were used instead, it would stand alone as a pronoun:

• これは仕事です = This is work / This is a job

So in this sentence, この仕事 is the natural way to say this work.

を marks the direct object of the verb. In other words, it marks the thing being acted on.

Here, the action is 終わらせよう = let’s finish / let’s bring to an end, so the thing being finished is:

• この仕事を = this job / this work

So the structure is:

• この仕事を = this job
• 終わらせよう = let’s finish it

A very literal breakdown would be:

• As for this job, let’s finish it quickly

But in natural English, that becomes something like Let’s finish this work quickly.

さっさと means something like:

• quickly
• without wasting time
• promptly
• get on with it

It often has a nuance of doing something efficiently and without delay. Depending on tone, it can also sound a little pushy, like:

• Come on, let’s get this done
• Let’s finish this already

So さっさと is not just neutral quickly in every case. It often suggests:

• no dawdling
• no hesitation
• let’s move

That is why this sentence can feel energetic, impatient, or determined depending on context.

終わらせよう is the volitional form of 終わらせる.

Breakdown:

• dictionary form: 終わらせる
• volitional form: 終わらせよう

The volitional form is often used to mean:

• let’s ...
• I’ll ... / I think I’ll ... depending on context

In this sentence, it most naturally means:

• Let’s finish it
• Let’s get this done

So grammatically, this is a casual invitation, suggestion, or statement of intention.

Good question. The difference is connected to transitivity and causation.

• 終わる = to end / to be over
  
  • intransitive
• 終わらせる = to finish something / to bring something to an end
  
  • transitive, causative-like

Since この仕事 is the thing being completed, Japanese often uses 終わらせる to express actively finishing it.

Compare:

• 仕事が終わる = the work ends / the work is finished
• 仕事を終わらせる = finish the work

終わろう can mean let’s end or let’s be done, but 終わらせよう more clearly expresses let’s finish this specific task.

These are related but not identical.

• 終わる
  = to end, to be over

  • 会議が終わる = The meeting ends

• 終える
  = to finish, to complete

  • 仕事を終える = finish the work
    This is a direct transitive verb and can sound a bit more formal or written in some contexts.

• 終わらせる
  = to bring something to an end, to get something finished

  • 仕事を終わらせる = finish the work
    This often emphasizes making sure it gets done.

In many situations, 仕事を終える and 仕事を終わらせる are both possible, but the nuance can differ slightly:

• 終える = complete
• 終わらせる = get it finished / bring it to completion

In this sentence, 終わらせよう sounds natural and active, especially with さっさと.

In this sentence, yes, 終わらせよう most naturally means let’s finish it.

But the volitional form can also express the speaker’s own intention:

• 帰ろう = I’ll go home / Let’s go home

Which meaning it has depends on context.

Here, because the sentence sounds like a suggestion directed toward a group or another person, it is usually understood as:

• Let’s quickly finish this work

So よう does not inherently mean only let’s; it can also mean I’ll or I think I’ll.

It is casual.

Clues:

• 終わらせよう is a plain-form volitional
• there is no です / ます
• さっさと can sound fairly direct

A more polite version would be something like:

• この仕事をさっさと終わらせましょう。

That means the same basic thing, but sounds more polite and appropriate in formal situations.

So the original sentence is something you might say:

• to a coworker you know well
• to a friend
• to yourself
• in an informal, direct context

Yes, it can, depending on tone and situation.

By itself, さっさと often carries a feeling of:

• hurry up
• get moving
• don’t waste time

So if you say it to someone above you, or if you say it sharply, it can sound rude or impatient.

For example, the sentence could sound like:

• Let’s quit dragging this out and finish it

But in a friendly or motivated tone, it can simply sound energetic:

• Come on, let’s get this done quickly

So the word itself is not automatically rude, but it is stronger and more forceful than a neutral adverb like 早く in some contexts.

Yes, but the nuance changes.

• 早く終わらせよう = let’s finish it early / quickly
• さっさと終わらせよう = let’s get it over with quickly / let’s stop wasting time and finish it

早く is more neutral and simply refers to speed.

さっさと adds a stronger feeling of:

• promptness
• efficiency
• impatience or decisiveness

So both are possible, but さっさと has more attitude.

Japanese nouns usually do not mark singular vs. plural the way English does, so 仕事 can mean different things depending on context:

• job
• work
• task
• piece of work

With この, it usually refers to a particular piece of work or assignment:

• この仕事 = this job / this task / this work

The best English translation depends on the situation:

• office context: this work
• assignment context: this task
• practical context: this job

So the Japanese itself is flexible.

No, normal Japanese writing usually does not use spaces between words like this.

Normally it would be written as:

• この仕事をさっさと終わらせよう。

Spaces are often added in learning materials to make the structure easier to read.

So for study purposes, this version helps you see the parts:

• この
• 仕事
• を
• さっさと
• 終わらせよう

But in real Japanese text, you normally will not see those spaces.

It sounds like the speaker is being:

• practical
• direct
• motivated
• possibly a little impatient

The combination of:

• さっさと = quickly, without wasting time
• 終わらせよう = let’s finish it

gives the sentence an energetic let’s get this over with feeling.

So depending on tone, it could sound like:

• encouraging
• determined
• slightly bossy
• annoyed that the task is still not done

That nuance comes more from さっさと and the casual form than from the basic meaning alone.