A control device for rotary machine includes: a voltage instruction generation section for generating a voltage instruction; a voltage application section for applying voltage to a rotary machine based on the voltage instruction; a current detection section for detecting rotary machine current of the rotary machine; and an inductance calculation section for calculating an inductance of the rotary machine from the voltage instruction and the rotary machine current. The voltage instruction generation section generates voltage instructions of constant DC voltages. The voltage application section applies voltages to the rotary machine based on the voltage instructions. The inductance calculation section calculates the inductance from a voltage instruction for measurement arbitrarily selected from the voltage instructions, and the rotary machine currents detected by the current detection section before and after application of the voltage instruction for measurement.