Practice JLPTHow to tell them apart
たとたん marks an immediate, often surprising reaction triggered the instant an action finishes, like ドアを開けた途端に猫が飛び出した. かと思うと frames two quick successive events the speaker observes, often with a sense of no sooner...than, like 雨が降ったかと思うとすぐやんだ. Swapping them is unnatural because たとたん needs one action directly causing an instant change, while かと思うと links two noticed events without that tight cause-effect bond.
- 途端（に） Use 途端（に） when one action instantly triggers a reaction or change the moment it happens.
- かと思うと Use かと思うと when you notice one event and then another follows right after it.
| Grammar point | Meaning | JLPT level |
|---|---|---|
| 途端（に） ni | The moment / as soon as | N2 |
| かと思うと kato uto | As soon as / no sooner than | N2 |
途端（に） ni
The moment / as soon as
The moment; just as; as soon as; then | A noun/adverb which expresses the idea that 'something occurred the moment someone did something or something took place'.
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その日本の写真を見た途端（に）家族に会いたくなった。
I wanted to see my family the moment I saw that Japanese photograph.
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その牛乳を飲んだら、途端に腹が痛み出した。
As soon as I drank the milk, my stomach started to ache.
かと思うと kato uto
As soon as / no sooner than
As soon as (one notices that) ~; soon after; when one thinks/feels that ~ | A phrase indicating that an action or state in the dependent clause occurs very closely with another action or state in the clause, or causes another action or state in the main clause.
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うちの小学生の子供は、テレビを見み終おわったかと思うと、コンピュータゲームをやり始める。
Our elementary school child starts to play computer games soon after he finishes watching TV.
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ハワイでは、雨が降ってきたかと思うと、すぐやんでしまう。
In Hawaii, as soon as it begins to rain, it stops right away.
途端（に） and かと思うと are both JLPT N2 grammar points that Japanese learners often mix up. This page compares them side by side — meanings, usage and example sentences — so you can tell them apart.