the moment; as soon as
私が抱いたとたん、赤ちゃんは泣き出した。
As soon as I picked up the baby, it started crying.
彼は病院へ行ったとたん息を引き取った。
He passed away as soon as he got to the hospital.
息子の死んだ知らせを聞いたとたん、彼女はわっと泣き出した。
As soon as she heard the news of her son's death, she burst into tears.
彼は娘が死んだ事を聞いたとたん、泣き崩れた。
As soon as he heard that his daughter had died, he broke down in tears.
私たちが出かけたとたん雨が降り始めた。
The moment we went out, it started to rain.
彼女はその知らせを聞いたとたん、突然泣き出した。
The moment she heard the news, she suddenly burst into tears.