A control device for an AC rotary machine, comprising: - a current vector detection section for detecting a detected current vector from current of an AC rotary machine; - a magnetic flux vector detection section for detecting a rotor magnetic flux vector from the detected current vector of the AC rotary machine and outputting the rotor magnetic flux vector as a detected magnetic flux vector; - an adaptive observation section for outputting an estimated current vector, an estimated magnetic flux vector, and an estimated position of the AC rotary machine; - a control section for outputting a voltage instruction vector so that the detected current vector coincides with a current instruction vector; - a voltage application section for applying voltage to the AC rotary machine, based on the voltage instruction vector; - a deviation vector calculation section for outputting a current deviation vector which is a deviation between the estimated current vector and the detected current vector, and a magnetic flux deviation vector which is a deviation between the estimated magnetic flux vector and the detected magnetic flux vector; and - a deviation amplification section for amplifying the current deviation vector and the magnetic flux deviation vector and outputting the amplified vectors as an amplified deviation vector, wherein - the adaptive observation section is adapted to calculate and output the estimated current vector, the estimated magnetic flux vector, and the estimated position, based on the voltage instruction vector and the amplified deviation vector, and - further, the control section is adapted to output a voltage instruction vector on which a high-frequency voltage vector having a frequency component different from a frequency for driving the AC rotary machine is superimposed, and the magnetic flux vector detection section is adapted to calculate an angular difference between an axis of the estimated magnetic flux vector and an axis of the rotor magnetic flux vector based on a magnitude of a high-frequency current vector having the same frequency component as the high-frequency voltage vector, included in the detected current vector, and calculate and output the detected magnetic flux vector, based on the angular difference and a magnitude of a rotor magnetic flux. - a current vector detection section for detecting a detected current vector from current of an AC rotary machine; - a magnetic flux vector detection section for detecting a rotor magnetic flux vector from the detected current vector of the AC rotary machine and outputting the rotor magnetic flux vector as a detected magnetic flux vector; - an adaptive observation section for outputting an estimated current vector, an estimated magnetic flux vector, and an estimated position of the AC rotary machine; - a control section for outputting a voltage instruction vector so that the detected current vector coincides with a current instruction vector; - a voltage application section for applying voltage to the AC rotary machine, based on the voltage instruction vector; - a deviation vector calculation section for outputting a current deviation vector which is a deviation between the estimated current vector and the detected current vector, and a magnetic flux deviation vector which is a deviation between the estimated magnetic flux vector and the detected magnetic flux vector; and - a deviation amplification section for amplifying the current deviation vector and the magnetic flux deviation vector and outputting the amplified vectors as an amplified deviation vector, - the adaptive observation section is adapted to calculate and output the estimated current vector, the estimated magnetic flux vector, and the estimated position, based on the voltage instruction vector and the amplified deviation vector, and - further, the control section is adapted to output a voltage instruction vector on which a high-frequency voltage vector having a frequency component different from a frequency for driving the AC rotary machine is superimposed, and the magnetic flux vector detection section is adapted to calculate an angular difference between an axis of the estimated magnetic flux vector and an axis of the rotor magnetic flux vector based on a magnitude of a high-frequency current vector having the same frequency component as the high-frequency voltage vector, included in the detected current vector, and calculate and output the detected magnetic flux vector, based on the angular difference and a magnitude of a rotor magnetic flux.