An electric power steering device, comprising: a motor configured to assist in controlling a driver's steering torque of a vehicle; and a control unit including inverter circuits (3a,3b) each including a plurality of switching elements, the control unit being configured to control drive of the motor, wherein the motor includes at least two independent sets of motor windings, wherein the control unit includes: a control part configured to calculate a current command value for driving the motor in a d-q-axis coordinate system; and an output part configured to drive the plurality of switching elements by a drive signal corresponding to the current command value, to thereby be capable of supplying currents to the at least two independent sets of motor windings independently of each other, and wherein the control part is configured to: detect a failure of each component of the electric power steering device; characterized in that the control part is further configured to restrict, when control is continued with field-weakening control by a normal one of the at least two independent sets of motor windings and a normal one of the inverter circuits (3a, 3b) depending on the detected failure, a d-axis current based on a torque ripple that occurs in a steering wheel of the vehicle with respect to the field-weakening control of a state in which the failure has not occurred. a motor configured to assist in controlling a driver's steering torque of a vehicle; and a control unit including inverter circuits (3a,3b) each including a plurality of switching elements, the control unit being configured to control drive of the motor, wherein the motor includes at least two independent sets of motor windings, wherein the control unit includes: a control part configured to calculate a current command value for driving the motor in a d-q-axis coordinate system; and an output part configured to drive the plurality of switching elements by a drive signal corresponding to the current command value, to thereby be capable of supplying currents to the at least two independent sets of motor windings independently of each other, and a control part configured to calculate a current command value for driving the motor in a d-q-axis coordinate system; and an output part configured to drive the plurality of switching elements by a drive signal corresponding to the current command value, to thereby be capable of supplying currents to the at least two independent sets of motor windings independently of each other, and wherein the control part is configured to: detect a failure of each component of the electric power steering device; characterized in that the control part is further configured to restrict, when control is continued with field-weakening control by a normal one of the at least two independent sets of motor windings and a normal one of the inverter circuits (3a, 3b) depending on the detected failure, a d-axis current based on a torque ripple that occurs in a steering wheel of the vehicle with respect to the field-weakening control of a state in which the failure has not occurred. detect a failure of each component of the electric power steering device; characterized in that the control part is further configured to restrict, when control is continued with field-weakening control by a normal one of the at least two independent sets of motor windings and a normal one of the inverter circuits (3a, 3b) depending on the detected failure, a d-axis current based on a torque ripple that occurs in a steering wheel of the vehicle with respect to the field-weakening control of a state in which the failure has not occurred.