An image forming apparatus that efficiently cools two circuit boards with one fan. An AC input circuit board has an AC power supply voltage supplied thereto from a commercial power supply, and includes a drive circuit for driving a heater. A power supply circuit board has an AC voltage supplied thereto from the AC input circuit board, and includes a conversion circuit for converting the AC voltage to a DC voltage. A sheet metal having a tubular shape covers the power supply circuit board. A fan cools the power supply circuit board. A duct member is arranged in a manner overlapping the sheet metal and cooperates with part of a wall portion of the sheet metal to form a flow passage for cooling the AC input circuit board with wind generated by the fan.