Every time: 〜たびに

〜たびに means “every time”: on each occasion the first thing happens, the second happens too. 京都に来るたびに、このお寺を訪れる, “every time I come to Kyoto, I visit this temple”.

• 京都に来るたびに、このお寺を訪れる。きょうとにくるたびに、このおてらをおとずれる。Every time I come to Kyoto, I visit this temple.
• この歌を聞くたびに、学生のころを思い出す。このうたをきくたびに、がくせいのころをおもいだす。Every time I hear this song, I remember my student days.
• 旅行のたびに、お土産を買いすぎてしまう。りょこうのたびに、おみやげをかいすぎてしまう。Every time I travel, I end up buying too many souvenirs.

たび means “time, occasion”. 〜たびに links two facts that recur together: every time A happens, B happens too. It's used to talk about habits, memories that come back, reactions that repeat — English “every time”, “whenever”.

• 母は電話のたびに、「ちゃんと食べてる？」と聞く。はははでんわのたびに、「ちゃんとたべてる？」ときく。Every time she calls, my mother asks, “Are you eating properly?”
• この道を通るたびに、昔のことを思い出す。このみちをとおるたびに、むかしのことをおもいだす。Every time I walk down this street, I think back to the past.

Verb in the dictionary form + たびに, even when talking about the past (it's the second part that carries the tense). Event noun + の + たびに. You can also say たび on its own, without に.

• 子どものころ、祖父に会うたびに、お小遣いをもらった。こどものころ、そふにあうたびに、おこづかいをもらった。As a child, every time I saw my grandfather, he'd give me pocket money.
• 試験のたびに、おなかが痛くなる。しけんのたびに、おなかがいたくなる。Every time there's an exam, I get a stomach ache.

〜と (N4) can also express a habit (春になると、花が咲く), but it rather describes an automatic consequence, like a law. たびに stresses repetition and each occasion one by one, often with feeling. ごとに (next point) is mostly used with regular units: 一時間ごとに, 一人ごとに.

• ボタンを押すと、ドアが開きます。ぼたんをおすと、どあがあきます。When you press the button, the door opens.