A control apparatus for an AC rotary machine, characterized by comprising: an AC rotary machine that includes a first winding and a second winding which have a phase difference and are not electrically connected to each other; a first current detection unit (4a, 4c) that detects a current of the first winding; a second current detection unit (4b, 4d) that detects a current of the second winding; a control unit that calculates a first voltage command and a second voltage command on the basis of a detected current value of the current of the first winding or the current of the second winding of the AC rotary machine; a first voltage application unit that applies a voltage to the first winding on the basis of the first voltage command; a second voltage application unit that applies a voltage to the second winding on the basis of the second voltage command; and a first detectability determination unit that determines a detectability of the current of the first winding, detected by the first current detection unit (4a, 4c), by determining whether or not the first voltage command and/or the second voltage command are within a predetermined range, characterised in that: the control unit calculates the first voltage command on the basis of the current of the first winding, detected by the first current detection unit (4a, 4c), when the first detectability determination unit determines that the current of the first winding is detectable, and calculates the first voltage command and the second voltage command on the basis of the current of the second winding, detected by the second current detection unit (4b, 4d), when the first detectability determination unit determines that the current of the first winding is undetectable. an AC rotary machine that includes a first winding and a second winding which have a phase difference and are not electrically connected to each other; a first current detection unit (4a, 4c) that detects a current of the first winding; a second current detection unit (4b, 4d) that detects a current of the second winding; a control unit that calculates a first voltage command and a second voltage command on the basis of a detected current value of the current of the first winding or the current of the second winding of the AC rotary machine; a first voltage application unit that applies a voltage to the first winding on the basis of the first voltage command; a second voltage application unit that applies a voltage to the second winding on the basis of the second voltage command; and a first detectability determination unit that determines a detectability of the current of the first winding, detected by the first current detection unit (4a, 4c), by determining whether or not the first voltage command and/or the second voltage command are within a predetermined range, characterised in that: the control unit calculates the first voltage command on the basis of the current of the first winding, detected by the first current detection unit (4a, 4c), when the first detectability determination unit determines that the current of the first winding is detectable, and calculates the first voltage command and the second voltage command on the basis of the current of the second winding, detected by the second current detection unit (4b, 4d), when the first detectability determination unit determines that the current of the first winding is undetectable. the control unit calculates the first voltage command on the basis of the current of the first winding, detected by the first current detection unit (4a, 4c), when the first detectability determination unit determines that the current of the first winding is detectable, and calculates the first voltage command and the second voltage command on the basis of the current of the second winding, detected by the second current detection unit (4b, 4d), when the first detectability determination unit determines that the current of the first winding is undetectable.