kono mise ha teisyoku ga yasukute oisii node, hiru ha itumo konzatusite imasu.

They are doing different jobs.

• この店は sets the overall topic: as for this restaurant...
• 定食が marks what is being described within that topic: the set meals are cheap and delicious.

So the structure is roughly:

• As for this restaurant, its set meals are cheap and tasty, so...

This is very common in Japanese: one thing is the big topic, and another thing inside that topic gets marked with が as the subject of a description.

You could say 定食は in some contexts, but 定食が is more natural here because it presents the set meals as the thing that has the qualities cheap and delicious.

A useful way to think about it:

• が: identifies what has the property
• は: introduces or contrasts a topic

Here, the sentence is already about この店は, so using 定食が fits well:
As for this restaurant, the set meals are cheap and delicious...

If you used 定食は, it might sound more contrastive, like as for the set meals...

Because this is the て-form of an い-adjective, used to connect adjectives.

• 安い → 安くて
• おいしい stays in its normal form at the end of the adjective chain

So:

• 安くておいしい = cheap and delicious

For い-adjectives, the rule is:

• remove the final い
• add くて

Examples:

• 高い → 高くて
• 新しい → 新しくて

When Japanese links adjectives, usually only the non-final ones take て-form.

So:

• 安くておいしい = correct
• the final adjective stays in plain form because it ends the adjective phrase

This works like cheap and delicious in English.
The first adjective connects forward, and the last one completes the description.

ので means because / since, and it gives a reason for what follows.

So this part:

• 定食が安くておいしいので

means:

• because the set meals are cheap and delicious

Then the result follows:

• 昼はいつも混雑しています
• it is always crowded at lunchtime

So the sentence structure is:

• Because A, B.

Both can mean because, but they feel a little different.

• ので: softer, more explanatory, often sounds more objective or polite
• から: more direct, more straightforward, sometimes more personal

In this sentence, ので fits nicely because it gives a calm explanation:

• Because the set meals are cheap and delicious, it is always crowded at lunchtime.

If you used から, the meaning would still be very similar, but the tone would be a bit more direct.

Here 昼は means something like:

• as for lunchtime
• at lunchtime

Using は makes 昼 a topic or time frame for the statement.

So:

• 昼はいつも混雑しています
• At lunchtime, it is always crowded.

If you used 昼に, it would sound more like a simple time point.
With は, there is often a slight feeling of setting the scene, and sometimes mild contrast, such as at lunchtime (especially), it’s crowded.

In Japanese, time words can often appear without に, and は is very common when the speaker wants to highlight that time period.

It is the ている form of 混雑する.

• 混雑する = to be crowded / to become crowded
• 混雑している = is crowded / is in a crowded state

Here, ている describes a continuing state, not just an action in progress.

So:

• 昼はいつも混雑しています
• It is always crowded at lunchtime.

This is a very common use of ている with verbs that describe a resulting state.

Yes, this is the polite form of いる as part of 〜ている.

• 混雑している = plain form
• 混雑しています = polite form

It is not the separate existential verb meaning to exist in the main sense of the sentence.
It is functioning as part of the grammar pattern 〜ている.

定食 usually means a set meal: a fixed meal combination commonly served at Japanese restaurants.

It often includes things like:

• rice
• soup
• a main dish
• side dishes

So this sentence is saying the restaurant’s set meals are cheap and delicious.

Literally, 店 is a broad word meaning shop/store/place of business.
But in context, because the sentence talks about 定食 and lunchtime crowds, restaurant or eatery is the natural English translation.

So:

• この店 literally: this shop / this establishment
• natural here: this restaurant

Because of the grammar:

• 定食が安くておいしい

The adjective phrase directly follows 定食が, so 定食 is what is cheap and delicious.

Then the whole reason clause explains why the restaurant gets crowded.

So the logic is:

1. As for this restaurant...
2. the set meals are cheap and delicious
3. therefore it is crowded at lunchtime

いつも means always.

It modifies the predicate:

• いつも混雑しています
• is always crowded

Its placement before the verb phrase is very natural in Japanese.
Adverbs like いつも, よく, たいてい often go before what they modify.

No, not grammatically.

The sentence does not say the restaurant itself is cheap and delicious.
It specifically says:

• 定食が安くておいしい
• the set meals are cheap and delicious

That is why the restaurant is crowded.

If Japanese wanted to say the restaurant itself is cheap, the wording would need to be different.

Because この is a demonstrative that directly modifies a noun.

So:

• この店 = this shop / this restaurant

This works like:

• この本 = this book
• この人 = this person

You do not put の or another particle between この and the noun.

Here it is read みせ.

So the beginning is:

• この店は = このみせは

That is the normal reading when 店 means shop/store/restaurant in everyday language.

Yes, in many situations that would be natural.

• 混雑しています = somewhat more formal or written-sounding
• 込んでいます = very common in everyday speech

So:

• 昼はいつも混雑しています
• 昼はいつも込んでいます

Both can mean It’s always crowded at lunchtime.

It separates the reason part from the main statement:

• 定食が安くておいしいので、
• 昼はいつも混雑しています。

This comma is helpful and very natural in writing, especially before or after a clause ending in ので.
Japanese punctuation is somewhat flexible, but here it makes the sentence easier to read.

A good way to break it down is:

• この店は — as for this restaurant
• 定食が — the set meals
• 安くておいしい — are cheap and delicious
• ので — because
• 昼は — at lunchtime
• いつも — always
• 混雑しています — is crowded

So the full pattern is:

• [Topic] は [subject] が [description] ので、 [time] は [adverb] [result].

This is a very common Japanese sentence structure:
topic + reason + result.