A blast mechanism in an image reading apparatus reliably cools heat generated in boards by a blast path with high cooling action among a plurality of boards disposed inside a casing. A partition plate is disposed between a plurality of boards disposed at a distance away in a layered shape, a first blast path is formed between a top of the casing and a first board, a second blast path is formed between the first board and the partition plate, a third blast path is formed between the partition plate and a second board, and a flow of cooling air is formed in each blast path with a blast fan. A blast mechanism for sending cooling air includes the casing, first and second boards disposed vertically inside the casing, the partition plate disposed between the first board and the second board, and fans for sending cooling air.