An electric motor control device that can accurately calculate the rotating speed of an electric motor. The electric motor control device includes a speed calculating unit configured to receive, from a position detector that detects a rotational position of an electric motor and outputs a position detection signal including a periodic error determined according to the rotational position, an input of the position detection signal, receive, from a time detector that outputs a position change time signal obtained by detecting a time period in which the position detection signal output from the position detector changes, an input of the position change time signal, and calculate rotating speed of the electric motor based on the position detection signal and the position change time signal. Further, there is a speed correcting unit for correcting a periodic speed error determined according to the rotational position of the electric motor.