In a cooling structure for a vehicle control unit in which semiconductor elements are housed in a case 34 made of a resin, such as a power distributor, a heat sink member 56 which is connected to the semiconductor elements in a heat transferable manner is disposed on an outer face of the case 34. A plurality of fins 56f are formed on a face of the heat sink member which is exposed to the outside of the case. Ribs 34f are formed on the outer face of the case. The ribs 34f cover end portions of the fins 56f in positions where the ribs are joined to the end portions of the fins, respectively.