A motor controller, an electric power steering device using the motor controller, and a vehicle using the motor controller are provided. Even if an abnormality occurs at a motor drive circuit or a multiphase electric motor, the motor controller is capable of continuously driving and controlling the electric motor. The motor controller includes plural hardware sets configured to operate in a normal state and to output a motor current, a control operation device configured to control the plurality of hardware sets commonly, an electric motor configured to operate with motor current output from each of the plurality of hardware sets, and an abnormality diagnosis unit configured to diagnose an abnormality of each of the plurality of hardware sets. In the control device, when there is an abnormal hardware set that has been diagnosed by the abnormality diagnosis unit, the control operation device stops an operation of the abnormal hardware set that has been diagnosed, and continues driving of the electric motor with a normal hardware set.