Provided is a rotating electric device control system having the function to boost the output of a DC power source. The system can suppress generation of an overcurrent by the DC power source when a transient voltage increase occurs upon start of boosting. The system includes: a frequency conversion unit which is arranged between the DC voltage power source and the rotating electric device and converts the output of the DC power source; a voltage conversion unit which is arranged between the DC power source and the frequency conversion unit and boosts the output of the DC power source in accordance with a boost instruction value; and a control unit for controlling the frequency conversion unit and the voltage conversion unit. The control unit performs switching from a non-boost control mode to a boost control mode when a target torque and an rpm of the rotating electric device exceed a predetermined transition boundary set in accordance with a correlation therebetween by using, as a reference, a boost-enabled power W3 obtained by subtracting a boost power transitionally generated during the switching from an allowable power which can be outputted from the DC power source. A switching boundary K3 is set in a region where the power consumption of the rotating electric device is not greater than the boost-enabled power WS.