An electric power steering drive system provided with a motor with its torque pulsation reduced, and a controller characterized by excellent manufacturability.The stator core of a motor is composed of an annular back core and a plurality of teeth created separately from the back core and secured on the inner periphery of the back core. An 8-pole/9-slot, 10-pole/9-slot or 10-pole/12-slot relationship is found between the number of the magnets of a rotor (number of poles) and the number of slots. The diameter of the stator coil is 1.0 mm or more. A motor controller comprises a power module, a conductor module and a control module. The terminal of the power module and the bus bar of the conductor module are connected by welding, whereas the terminal of the power module and terminal of the control module are connected by soldering.