The motor driving device includes a plurality of control system for supplying individually drive current to the plurality of coil groups contained in the motor. Motor drive unit sets the current command value separately for each control system. Then, supplies on the basis of the current command value set for each control system, by providing a drive instruction to the driving circuit of the inverter, the drive current from the inverter to the coils. Further, the motor driving device detects a failure of inverter or coil groups for each control system, only the operation of the failed control system is stopped or degenerated. Further, the motor driving device includes a main operation unit and the spare computing device. Thus, the main operating unit even fails, if it is normal preliminary operation device, it is possible to continue the driving of the motor by using a part of the control system.
.FIELD 8