adverb
just as; right after; as soon as; at that moment
Used after a verb in the past tense or a noun to indicate that something happens immediately after the preceding action or state. Often implies an unexpected or sudden result.
家を出た途端に雨が降り出した。
Just as I left the house, it started raining.
彼はその話を聞いた途端に笑い出した。
He burst out laughing the moment he heard that story.