A control apparatus includes a first determination section determining whether a power-supply voltage has decreased below a first threshold value, an interruption section interrupting a current flow to an inverter if the voltage has decreased below the first threshold value, a second determination section that determining whether the power-supply voltage has increased above a second threshold value, an interruption releasing section releasing the interruption based on the fact that the voltage has increased above the second threshold value, a count section counting the number of interruptions, a limiting section determining whether the decrease in the power-supply voltage is caused by a first factor of an electric rotating machine or a second factor, and limits the counting if the decrease in the power-supply voltage is caused by the second factor, and a third determination section determining whether the interruption is allowed to be released based on the number of interruptions.