To provide an electric power steering device capable of coping with the increased current of a motor and the downsizing of a controller, and suppressing a driver's burden of steering force.

Corresponding to a steering torque detected by a steering torque detector for detecting the steering torque, a controller 15 for controlling a motor that gives steering assisting power to a steering system of a vehicle includes a cover 41, a control substrate 42 on which electric components 52 are mounted, an insert base 43 electrically connected to the control substrate 42, a metal substrate 44 on which heat-generating electric components 55, 56 are mounted and which is electrically connected to the insert base 43, and a heat sink 45 in a layered structure. Further, a fan 46 is provided on the heat sink 45.