To prevent the deterioration of the time-base resolution of the measurement of rotational speed due to rotational speed in a discrete time system for controlling a rotary machine, by updating a control input to the rotary machine at the time intervals of a sampling time.

A rotational-speed measuring means 202 measures rotational speed on the basis of the time intervals of a pulse signal from a pulse generating means 201, and a control means 300 controls a control input to the rotary machine 200 by a discrete time system on the basis of the rotational speed. The rotational-speed measuring means 202 measures rotational speed from the time intervals of a pulse signal immediately before a time when the control input is updated and a pulse signal immediately after the updated time, a sample-time setting means 301 of the control means 300 sets time intervals obtained by multiplying the time intervals of the pulse signal by an integer of 1 or more as a sampling time, a control-input processing means 302 updates the control input corresponding to rotational speed and the sampling time, and a control-input update means 303 updates the control input to the rotary machine 200 at the time intervals of the sampling time at that time.