An open part that has an opening surface that is perpendicular to the horizontal direction is formed in a housing of a vehicle control device. An interior of the housing is divided into a first space including the open part and a second space by a partitioning member, a main surface thereof having a hole formed therein and opposing the opening surface. The semiconductor cooling unit is housed in the first space. The semiconductor cooling unit is detachably attached in a direction in which the opening surface and the partitioning member oppose each other. An engaging member arranged on the cover of the semiconductor cooling unit engages a guide arranged on the housing, and the guide supports weight of the semiconductor cooling unit. A heat sink is provided on a base plate and forms a vertically-directed flow passage.