A control device for a rotary machine, comprising: an AC rotary machine having a rotor structure for generating saliency, and including first three-phase windings and second three-phase windings; a first current detector configured to detect a current flowing through each of the first three-phase windings as a first winding current; a second current detector configured to detect a current flowing through each of the second three-phase windings as a second winding current; a controller (10, 11) configured to calculate a first voltage command so that the first winding current detected by the first current detector matches a first current command, which is a command value directed to the first winding current, and to calculate a second voltage command so that the second winding current detected by the second current detector matches a second current command, which is a command value directed to the second winding current; a first power converter configured to apply a voltage to each phase of the first three-phase windings based on the first voltage command; a second power converter configured to apply a voltage to each phase of the second three-phase windings based on the second voltage command; a position estimation command generator (14, 15, 301, 302) configured to generate a first position estimation command having a first frequency, and to generate a second position estimation command having the first frequency; and a rotation position estimator configured to extract an amplitude value of a component of the first frequency based on at least one of the first winding current or the second winding current, to thereby estimate a rotation position of the AC rotary machine based on a magnitude of the amplitude value, wherein: the controller (10, 11) is configured to superimpose the first position estimation command on the first voltage command to output a result of superimposition to the first power converter, and to superimpose the second position estimation command on the second voltage command to output a result of superimposition to the second power converter characterized in that the position estimation command generator is configured to output the first position estimation command and the second position estimation command while providing a phase difference between the first position estimation command and the second position estimation command. an AC rotary machine having a rotor structure for generating saliency, and including first three-phase windings and second three-phase windings; a first current detector configured to detect a current flowing through each of the first three-phase windings as a first winding current; a second current detector configured to detect a current flowing through each of the second three-phase windings as a second winding current; a controller (10, 11) configured to calculate a first voltage command so that the first winding current detected by the first current detector matches a first current command, which is a command value directed to the first winding current, and to calculate a second voltage command so that the second winding current detected by the second current detector matches a second current command, which is a command value directed to the second winding current; a first power converter configured to apply a voltage to each phase of the first three-phase windings based on the first voltage command; a second power converter configured to apply a voltage to each phase of the second three-phase windings based on the second voltage command; a position estimation command generator (14, 15, 301, 302) configured to generate a first position estimation command having a first frequency, and to generate a second position estimation command having the first frequency; and a rotation position estimator configured to extract an amplitude value of a component of the first frequency based on at least one of the first winding current or the second winding current, to thereby estimate a rotation position of the AC rotary machine based on a magnitude of the amplitude value, wherein: the controller (10, 11) is configured to superimpose the first position estimation command on the first voltage command to output a result of superimposition to the first power converter, and to superimpose the second position estimation command on the second voltage command to output a result of superimposition to the second power converter characterized in that the position estimation command generator is configured to output the first position estimation command and the second position estimation command while providing a phase difference between the first position estimation command and the second position estimation command. the controller (10, 11) is configured to superimpose the first position estimation command on the first voltage command to output a result of superimposition to the first power converter, and to superimpose the second position estimation command on the second voltage command to output a result of superimposition to the second power converter characterized in that the position estimation command generator is configured to output the first position estimation command and the second position estimation command while providing a phase difference between the first position estimation command and the second position estimation command.