A motor control device comprising: a motor electric angle initial value estimation unit that, when a motor electric angle detection unit that detects a motor electric angle of a multi-phase electric motor that generates a steering assist force is diagnosed as being abnormal in an initial diagnosis after a system restart, estimates an initial value of the motor electric angle on a basis of a response output of the multi-phase electric motor in response to input of a motor drive signal to the multi-phase electric motor; and a steering angle detection unit that detects a steering angle of a steering, characterized by a motor electric angle estimation unit that calculates the motor electric angle θme according to formula: θme = θos x RGr x P + θoff, wherein θos is an output shaft rotational angle detection value which is the steering angle detected by the steering detection unit, RGr is a deceleration ratio, P is a number of pole pairs, and θoff is estimated based on a motor angle origin θmd which is estimated by the initial value of the motor electric angle estimated by the motor electric angle value estimation unit, and a reference value θosr is obtained by multiplying an output shaft rotation angle detection value upon system start by the number P of pole pairs and the deceleration ratio RGr; and a motor drive control unit that, when the motor electric angle detection unit is normal, drive-controls the multi-phase electric motor on a basis of the motor electric angle detected by the motor electric angle detection unit, and when the motor electric angle detection unit is diagnosed as being abnormal in the initial diagnosis after the system restart, drive-controls the multi-phase electric motor on a basis of a motor electric angle estimation value estimated by the motor electric angle estimation unit. a motor electric angle initial value estimation unit that, when a motor electric angle detection unit that detects a motor electric angle of a multi-phase electric motor that generates a steering assist force is diagnosed as being abnormal in an initial diagnosis after a system restart, estimates an initial value of the motor electric angle on a basis of a response output of the multi-phase electric motor in response to input of a motor drive signal to the multi-phase electric motor; and a steering angle detection unit that detects a steering angle of a steering, characterized by a motor electric angle estimation unit that calculates the motor electric angle θme according to formula: θme = θos x RGr x P + θoff, wherein θos is an output shaft rotational angle detection value which is the steering angle detected by the steering detection unit, RGr is a deceleration ratio, P is a number of pole pairs, and θoff is estimated based on a motor angle origin θmd which is estimated by the initial value of the motor electric angle estimated by the motor electric angle value estimation unit, and a reference value θosr is obtained by multiplying an output shaft rotation angle detection value upon system start by the number P of pole pairs and the deceleration ratio RGr; and a motor drive control unit that, when the motor electric angle detection unit is normal, drive-controls the multi-phase electric motor on a basis of the motor electric angle detected by the motor electric angle detection unit, and when the motor electric angle detection unit is diagnosed as being abnormal in the initial diagnosis after the system restart, drive-controls the multi-phase electric motor on a basis of a motor electric angle estimation value estimated by the motor electric angle estimation unit.