To provide a controller for rotary electric machine apparatus which can calculate the voltage command value of the converter which reduces power loss with good accuracy, in the case where the normal modulation control and the overmodulation control are switched and performed. A controller for rotary electric machine apparatus sets a system voltage that power loss becomes the minimum as the converter voltage command value, based on a power loss characteristics of the normal modulation control which is a power loss characteristics of at least the inverter with respect to the system voltage in performing the normal modulation control, and a power loss characteristics of the overmodulation control which is a power loss characteristics of at least the inverter with respect to the system voltage in performing the overmodulation control.