A rotary machine control device includes a current detector to detect a rotary machine current flowing through a rotary machine, a position estimator to estimate a rotor position, a controller to output a rotary machine voltage instruction for driving the rotary machine on the basis of the rotary machine current and the rotor position, and a voltage applicator to apply a voltage to the rotary machine on the basis of the rotary machine voltage instruction. The position estimator estimates the rotor position from a flux linkage inductance variable component produced by an inductance variable component and the rotary machine current.