To provide a vehicle-mounted power converter for achieving miniaturization of itself without impairing heat dissipation performance.

A charger 210 is mounted on an upper surface 111 of a heat sink 110, and a DC-DC converter 310 is mounted on a lower surface 112 (rear surface) of the heat sink. With this configuration, the main amount of heat is supplied from the surface 111 of a charger side during charging (not running), and the main amount of heat is supplied from the surface 112 of the DC-DC converter side during running. Accordingly, the position of a heat source to be supplied to the heat sink 110 is changed depending on whether the vehicle is being charged or running, and the high amount of heat is not simultaneously supplied from both the surfaces. Thus, the amount of heat generation is reduced on one surface of the heat sink, so that a heat dissipation area can be sufficiently ensured in accordance with the reduction, and scale-up of the heat sink 110 can be avoided.