In a power supply device 1, a first space R1 and a second space R2 are delimited, a coil component 20 is arranged in the first space R1, and heat-generating components and components having weak resistance to heat are arranged in the second space R2. The power supply device 1 is configured to contain the coil component 20 in the first space R1 so that ambient air of the coil component 20 can contact a first side wall 72, which constitutes the first space R1, making it possible to expect discharge of heat to coolant in a coolant channel W via the first side wall 72. Therefore, heat can be discharged from the ambient air of the coil component, the temperature of which has been raised by heat generation, towards the coolant efficiently.