A driver device has a rear frame end disposed on an axial end of a motor, a heat sink on which a power module is fastened, and a connector case disposed on an outside of the heat sink having a first connector and a second connector for an external connection. A plate is fastened onto the connector case, with a motor-facing contact face of the plate contacting the rear frame end and a motor-facing-away contact face of the plate contacting the heat sink. Heat conductivity of the plate is equal to or greater than that of the rear frame end and that of the heat sink combined. Thus, a gap between the rear frame end and the heat sink is sealed and heat from the heat sink on which the power module is fastened is appropriately transmitted to the rear frame end.