tuutyou wo mitara, omotta yori zandaka ga sukunakute odorokimasita.

見たら is the -たら conditional form of 見る.

Here it means something like:

• when I looked
• after I looked
• upon looking

So 通帳を見たら means when I looked at my bankbook.

Why -たら?

• It often introduces something that happened after doing the first action.
• It can also carry a slight sense of discovery: when I looked, I found that...

That fits this sentence well, because the speaker checked the bankbook and then realized something surprising.

Compare:

• 通帳を見て、驚きました = I looked at the bankbook and was surprised.
• 通帳を見たら、驚きました = When I looked at the bankbook, I was surprised / Upon looking at it, I was surprised.

The -たら version sounds more natural here because it sets up the result of the discovery.

を marks the direct object of the verb 見る.

So:

• 通帳 = bankbook / passbook
• 通帳を見たら = when I looked at the bankbook

This is standard because 見る usually takes を for the thing being looked at.

通帳 is a bankbook or passbook.

In Japan, this is a small booklet issued by a bank that records account activity such as:

• deposits
• withdrawals
• current balance

So the sentence is talking about checking that bankbook and seeing the balance.

Yes. 思ったより means than I thought or than I expected.

Literally:

• 思った = thought
• より = than

In full, it might be something like:

• 思ったより残高が少ない
• The balance is lower than I thought

Japanese often leaves out words that are understood from context, so after より, the compared item is not repeated.

This pattern is very common:

• 思ったより高い = more expensive than I thought
• 思ったより簡単だった = easier than I thought
• 思ったより人が多い = more people than I expected

残高 is the thing being described as 少ない, so it takes が.

• 残高 = balance
• 少ない = few / little / low in amount

In Japanese, adjectives like 少ない often use が for what has that quality.

So:

• 残高が少ない = the balance is low / there isn’t much balance

Why not を?

• を marks the direct object of a verb.
• But 少ない is an adjective, not a transitive verb.

Why not は?

• は is possible in some contexts if you want to make 残高 the topic.
• But here, が simply presents the balance as the thing that turned out to be low.

So 残高が少なくて驚きました sounds very natural.

少なくて is the て-form of the adjective 少ない.

Here it links the reason to the result:

• 残高が少なくて驚きました
• I was surprised because the balance was low.

So ～て is being used in a reason/cause sense.

Why not 少ないで?

• ないで is mainly used with verbs, not い-adjectives.
• 少ない is an adjective, so its connector form is 少なくて.

Why not 少なかった?

• 少なかった is plain past: was low.
• You could say 残高が少なかったので驚きました, but that is a different structure using ので.
• In this sentence, 少なくて smoothly connects the cause to 驚きました.

In this sentence, 少ない is best understood as low or not much.

With 残高 (balance), English naturally says:

• the balance was low
• there wasn’t much money in the account

Japanese uses 少ない because the amount is small.

So although 少ない often gets translated as few or little, here the most natural English sense is low.

驚きました means I was surprised.

The sentence is not only stating a fact about the balance. It is also telling you the speaker’s emotional reaction.

Compare:

• 残高が少なかったです。 = The balance was low.

• 残高が少なくて驚きました。 = The balance was low, so I was surprised.

So 驚きました makes the sentence more personal and expressive.

The subject is understood to be the speaker: I.

Japanese often omits subjects when they are obvious from context.

So this sentence naturally implies:

• I looked at my bankbook
• the balance was lower than I had thought
• I was surprised

You do not need to say 私は unless you want extra emphasis or contrast.

A fuller version could be:

• 私は通帳を見たら、思ったより残高が少なくて驚きました。

But in normal Japanese, leaving out 私は sounds very natural.

They are very close, but 思っていたより can sound a little more explicit.

• 思ったより = than I thought
• 思っていたより = than I had been thinking / than I had expected

In many everyday sentences, they are almost interchangeable.

Here:

• 思ったより残高が少なくて驚きました
• 思っていたより残高が少なくて驚きました

Both are natural. The second one may slightly emphasize that the speaker had a prior expectation before checking.

Japanese often places comparison phrases before the thing being described.

So:

• 思ったより = than I thought
• 残高が少ない = the balance is low

Together:

• 思ったより残高が少ない
• The balance is lower than I thought

This word order is very normal in Japanese. The comparison phrase comes first, then the statement it modifies.

Yes, that is a very natural translation.

Other natural English versions include:

• When I checked my bankbook, I was surprised because the balance was lower than I thought.
• I looked at my bankbook and was surprised to see that the balance was lower than expected.
• Upon checking my bankbook, I was surprised that I had less money than I thought.

All of these capture the grammar and feeling of the Japanese sentence well.

It is a mix of plain and polite forms, which is very common in Japanese.

Inside the sentence:

• 見たら = plain form
• 思った = plain form
• 少なくて = plain connective form
• 驚きました = polite past

This is normal because only the final verb often needs to be polite in a complete sentence.

So the overall sentence is polite because it ends with 驚きました.

A more casual version would be:

• 通帳を見たら、思ったより残高が少なくて驚いた。

A fully polite-sounding version is possible, but less common and often heavier:

• 通帳を見ましたら、思ったより残高が少なくて驚きました。

In everyday speech and writing, the original sentence sounds natural.