A switching power supply includes a switching circuit, a main transformer, a rectifier circuit, and an output smoothing circuit, which are mounted on a base plate. Voltage transformation of an inputted direct current voltage is performed through collaboration among the above. A pedestal portion is formed on the base plate, and a channel to cool down electronic parts such as a diode is formed inside the pedestal portion. Since the channel is thus formed inside the pedestal portion, the device will not be larger-sized even when the channel is formed. Moreover, at least any of a switching element and a diode is mounted on the pedestal portion, and a choke coil is mounted in a region other than a region where the pedestal portion is formed. Therefore, even with the pedestal portion, it is significantly suppressed for the device to be larger-sized.