kono hon ha zaiko ga nakereba, toriyose wo onegaisimasu.

They are doing different jobs.

• この本は = as for this book
• 在庫がなければ = if there is no stock

So は marks the overall topic, while が marks the thing that specifically exists / does not exist, which is 在庫.

A natural way to understand the structure is:

• この本は → speaking about this book
• 在庫がなければ → if stock is not available
• 取り寄せをお願いします → please order it in

English often uses just one subject, but Japanese commonly separates the topic and the subject inside a clause like this.

なければ means if there is not / if it does not exist.

In this sentence, it comes from:

• 在庫がない = there is no stock / it is out of stock

Then that becomes the conditional:

• 在庫がなければ = if there is no stock

This -なければ pattern is a common way to make if clauses from negative forms.

A few similar examples:

• 時間がなければ = if there is no time
• 分からなければ = if you do not understand
• 行かなければ = if someone does not go

So here it simply means if it isn’t in stock.

Because 在庫 is the natural word for stock / inventory / items currently available in the store.

• 本がない could mean there is no book
• 在庫がない specifically means it is not in stock

In a shopping or bookstore situation, 在庫 is much more precise and natural. It tells you the issue is not that books in general do not exist, but that the store does not currently have this item available.

取り寄せ means ordering something in or having it brought in from elsewhere.

It is often used when a store does not currently have an item, but can get it from:

• another branch
• a warehouse
• the publisher
• a supplier

So in this sentence, 取り寄せ is not just a general purchase like buying. It means please arrange for the store to get this book for me.

Here, 取り寄せ is being treated like the action that is being requested.

• お願いします = please do / please arrange / please handle
• 取り寄せをお願いします = please arrange an order / please order it in

The を marks 取り寄せ as the thing being requested.

This is very common in polite Japanese:

• 確認をお願いします = please check
• 連絡をお願いします = please contact me / please make contact
• 対応をお願いします = please handle it

So 取り寄せをお願いします is a polite, businesslike way to say please order it in.

Yes. The thing being ordered is understood from the topic: この本.

Japanese often leaves out information that is already clear from context. Since the sentence begins with この本は, the listener understands that the requested 取り寄せ is for this book.

So even though it does not explicitly repeat この本を, the meaning is still:

• If this book is not in stock, please order this book in.

Japanese avoids repeating obvious information more than English does.

Because Japanese often omits the subject when it is obvious from context.

Here, the speaker is clearly talking to a store employee or bookstore staff member, so there is no need to say:

• あなたは
• 店員さんは
• お店は

The person being asked is understood.

This is very normal in Japanese. In English, we usually say please order it, where you is understood. Japanese does the same kind of thing even more often.

It is polite and appropriate, especially in a customer-service situation.

お願いします is a very common polite request form. It sounds softer and more businesslike than a direct command.

So this sentence is suitable for speaking to store staff.

If you wanted to sound even softer or more tentative, you could say something like:

• この本、在庫がなければ、取り寄せをお願いできますか。
• この本、在庫がなければ、取り寄せてもらえますか。

But 取り寄せをお願いします is already polite and natural.

Yes, this is the normal Japanese pattern.

Japanese very often puts the condition first, then the main request or result after it:

• 在庫がなければ、取り寄せをお願いします。
• 時間があれば、来てください。
• 分からなければ、聞いてください。

So the sentence structure is:

1. condition: if it is not in stock
2. request: please order it in

This is very standard and natural.

Yes. 在庫がありませんでしたら is more formal and more explicitly polite.

Compare:

• 在庫がなければ = if there is no stock
• 在庫がありませんでしたら = if there is no stock / if it is not available

Both are correct. The second one sounds more formal because it uses ありません, the polite form of ない.

In everyday polite conversation, なければ is still very common and does not sound rude.

Yes, it is natural and understandable.

It sounds like something a customer might say to bookstore staff. It is polite and practical.

A few small variations that are also natural are:

• この本は、在庫がなければ取り寄せをお願いします。
• この本、在庫がなければ取り寄せをお願いします。
• この本が在庫になければ、取り寄せをお願いします。

The original sentence is perfectly fine. The main thing it expresses is:

• Regarding this book, if it is not in stock, please order it in.

No. Standard Japanese is normally written without spaces.

So this would usually be written as:

この本は在庫がなければ、取り寄せをお願いします。

Spaces are often added in teaching materials to make it easier for learners to see the parts of the sentence.

So the spaces are just a study aid, not normal spelling.