My guess is you have Cedar Apple Rust (CAR), a very common apple leave disease esp. in wet spring. Please google pictures of apple leaves affected by CAR to see if they look like yours.

Where are you located? Telling us your zone and your location is helpful information.

Fungicide with ingredient such as myclobutanil or chlorothalonil is used to combat CAR effectively. The one I use is called Immunox (myclo) made by Spectracide. There are a couple of Immunox products on the market. Make sure you read the label that says for fruit trees.