kare ha sassato heya wo deta.

は marks 彼 as the topic of the sentence.

So 彼は means something like as for him or he in natural English.
It does not exactly mean the same thing as an English subject marker; it sets up what the sentence is about.

In this sentence:

• 彼は = as for him / he
• さっさと = quickly / without hesitation
• 部屋を = the room
• 出た = left / went out

So the structure is roughly:

As for him, he quickly left the room.

Grammatically, 彼 means he. However, in natural Japanese, pronouns like 彼 are often omitted if the person is already clear from context.

So this sentence is perfectly correct, but in real conversation, Japanese speakers might simply say:

さっさと部屋を出た。

if it is already obvious who left.

Also, 彼 can sometimes sound a little more explicit or written than English he. Japanese often prefers leaving subjects unstated when possible.

さっさと is an adverb meaning something like:

• quickly
• promptly
• without wasting time
• without hesitation

Depending on context, it can also carry a nuance like:

• briskly
• in a hurry
• get it over with
• sometimes even in an impatient way

So 彼はさっさと部屋を出た suggests he did not linger. He left promptly and decisively.

It often has a bit more nuance than a plain quickly.

Compared with a more neutral adverb like 速く or 早く, さっさと often suggests:

• doing something efficiently
• not hanging around
• moving on right away

In some contexts, it can sound slightly impatient:

• さっさと行って！ = Go already! / Hurry up and go!

But in your sentence, it simply gives the feeling that he left promptly.

This is a very common question.

Yes, を often marks the direct object, but with some motion verbs it can also mark the place that someone moves through or leaves.

So in:

部屋を出た

部屋を does not mean the room is a direct object in the English sense. Instead, を marks the location being exited.

This pattern is common with verbs like:

• 道を歩く = walk along the road
• 橋を渡る = cross the bridge
• 部屋を出る = leave the room

So here, を marks the space he leaves.

Yes, 部屋から出た is also correct.

The difference is mainly in focus:

• 部屋を出た = left the room
• 部屋から出た = came/went out from the room

を with 出る is very common and natural when talking about leaving a place.
から emphasizes the starting point or source a bit more.

In many situations, both are possible, but 部屋を出た is especially standard for leave the room.

The dictionary form is 出る.

This is an ichidan verb. Its past plain form is made by replacing る with た:

• 出る → 出た

So:

• 出る = to leave / to go out
• 出た = left / went out

出た is the plain past form.
出ました is the polite past form.

Both are correct, but they are used in different situations:

• 彼はさっさと部屋を出た。
  plain style; common in casual speech, narratives, and written storytelling

• 彼はさっさと部屋を出ました。
  polite style; used when speaking politely

The plain form is especially common in novels and casual description.

Because 出た is past tense, the sentence describes a completed action: he left the room.

If you used the non-past form:

彼はさっさと部屋を出る。

it could mean:

• he leaves the room
• he will leave the room
• in narrative style, he leaves the room

But 出た clearly tells you the action already happened.

Both can be possible in Japanese, but they create different emphasis.

• 彼はさっさと部屋を出た。
  As for him, he left the room quickly.
  This is a neutral topic-comment statement.

• 彼がさっさと部屋を出た。
  This puts more focus on him as the one who did it. It may sound contrastive or answer a question like Who left the room quickly?

So は is natural when you are simply talking about him and saying what he did.

Yes, Japanese word order is fairly flexible, as long as the particles make the roles clear.

For example:

• 彼はさっさと部屋を出た。
• 彼は部屋をさっさと出た。

Both are possible.

However, some orders sound more natural than others, and the original sentence is very natural. In Japanese, the verb usually comes at the end, but adverbs like さっさと can move around somewhat.

Yes, very often.

Japanese frequently omits subjects and topics when they are understood from context. So if everyone already knows who is being discussed, you could simply say:

さっさと部屋を出た。

This is one reason Japanese can sound less explicit than English. English usually needs a subject like he, but Japanese often does not.

In this sentence:

• は is written ha but pronounced wa when used as a particle
• を is usually pronounced o

So the sentence is pronounced roughly:

kare wa sassato heya o deta

This is a very common thing for learners to notice: particle pronunciation does not always match the basic kana sound.

部屋 usually means room, but depending on context it can also mean:

• a room in a house
• a private room
• a compartment or enclosed space

In this sentence, the normal meaning is simply room.

So 部屋を出た is the standard way to say left the room.

A very literal breakdown is:

• 彼 = he
• は = topic marker
• さっさと = quickly / promptly / without delay
• 部屋 = room
• を = marks the place exited
• 出た = exited / left

So a very literal gloss would be:

As for him, promptly, room-from-exit did

More natural English is:

He quickly left the room.