kono sinseisyo ha, siyakusyo no syorui ni site ha yomi yasui.

にしては means for..., considering..., or despite being..., with a nuance of this is a little surprising or better/worse than expected.

So:

• 市役所の書類にしては読みやすい = It’s easy to read for a city hall document = It’s easier to read than you’d expect from city hall paperwork

The important nuance is that the speaker seems to assume city hall documents are usually not very easy to read.

The は marks この申請書 as the topic of the sentence.

So the structure is basically:

• As for this application form, ...
• ... for a city hall document, it is easy to read.

Japanese often sets up a topic first, then comments on it. Here, the sentence is talking about this application form and saying something about it.

It is related, but in this sentence you should really treat にしては as a set expression.

So:

• この申請書は → the main topic marker
• 書類にしては → a grammar pattern meaning for a document / considering it is a document

In other words, don’t try to interpret にしては word by word too literally at first. It is best learned as one chunk.

市役所 means city hall / municipal office.
書類 means documents / paperwork.

So 市役所の書類 means:

• city hall documents
• documents from city hall
• municipal paperwork

The の connects the two nouns, showing that the documents belong to, come from, or are associated with city hall.

Here, この申請書 is being viewed as one example of that larger category.

Because やすい attaches to the verb stem, not the dictionary form.

• 読む → verb dictionary form
• 読み → verb stem
• 読みやすい → easy to read

This pattern is very common:

• 食べる → 食べやすい = easy to eat
• 分かる → 分かりやすい = easy to understand
• 使う → 使いやすい = easy to use

So 読みやすい is the normal and correct form.

It behaves like an い-adjective.

Even though it comes from the verb 読む, once you add やすい, the whole expression acts like an adjective:

• 読みやすい = easy to read
• 読みやすくない = not easy to read
• 読みやすかった = was easy to read

So in this sentence, 読みやすい is describing この申請書.

It is usually mild praise, not dramatic praise.

Because of にしては, the sentence sounds like:

• For this kind of document, it’s surprisingly readable
• This is better than I expected

It can sound slightly backhanded, because it implies something like:

• City hall documents are usually hard to read
• But this one is relatively good

So it is positive, but with a comparison against a low expectation.

You could say 市役所の書類としては読みやすい, and it would mean something like:

• As city hall documents go, it is easy to read

But the nuance is a little different.

• にしては = contrary to expectation / surprisingly
• としては = as for / in the category of / from the standpoint of

So にしては is better if you want the feeling of better than expected.
としては sounds more neutral and classificatory.

The comma is mostly there to make the sentence easier to read.

Japanese commas are more flexible than English commas. Here it helps separate:

• the topic: この申請書は、
• the comment: 市役所の書類にしては読みやすい。

You could often write the sentence without that comma and it would still be grammatically fine.

A natural polite version is:

• この申請書は、市役所の書類にしては読みやすいです。

The grammar is the same; only the ending becomes polite with です.

The original sentence ends in plain style, which is common in neutral writing, casual comments, or informal explanation.