A motor controller, which is inexpensive and has small size, is provided by reducing the size of a heat sink used in the motor controller and the number of all parts of the motor controller, wherein said motor controller includes a heat sink, a power semiconductor modules that is in close contact with the heat sink, a substrate (4) that is electrically connected to the power semiconductor module, and a fan (6) that generates the flow of external air and supplies cooling air to the heat sink, wherein said heat sink is formed by combining two kinds of heat sinks, which include a first heat sink (7) and a second heat sink (8), so as to conduct heat therebetween, and, wherein said power semiconductor module is in close contact with the second heat sink (8).