Motor controlling device

A motor control device includes a motor-speed detection unit detecting and outputting a detected motor speed based on an output signal of an encoder connected to a motor that is a synchronous motor; a motor electric-angle detection unit detecting and outputting a detected motor electric angle based on the output signal; a motor electric-angle estimation unit receiving a motor voltage, a motor current, and the detected motor speed, and estimating and outputting an estimated motor electric angle based on the motor voltage and the motor current; and a switching unit receiving the detected motor electric angle and the estimated motor electric angle, determining whether the encoder is operating normally based on the detected motor electric angle and the estimated motor electric angle, outputting the detected motor electric angle when the encoder is operating normally, and outputting the estimated motor electric angle when the encoder is not operating normally.