In a cooling device of an image forming apparatus, a space is formed between a flat surface of a sheet metal attached on a circuit board attached part and a power source circuit board. A duct is formed by a shielding member formed in a U shape surrounding the space, and on the lower part of the flat surface of the sheet metal, a tubular part as an air outlet is formed so as to be elongated to the side of a main body. On the upper part of the sheet metal arranged in a vertical direction, a fan motor is mounted, which sends cooled air into the power source circuit board and the duct. The cooled air cools the power source circuit board and also cools a power source unit in the main body via the tubular member.