A control system for controlling an electric rotating machine includes an inverter for driving the electric rotating machine, a converter that converts an input voltage thereof to an output voltage equal to a step-up command value, and supplies the output voltage to the inverter, a pulse generation section that generates PWM pulses from a carrier for controlling the inverter in accordance with result of comparison between the carrier and a voltage command to the electric rotating machine, and a command generation section that generates the step-up command value. The command generation section includes a command control section that controls the step-up command value such that a modulation factor defined as an amplitude of the voltage command divided by the output voltage of the converter is changed within a predetermined modulation factor range.