An ECU has a main IC and at least one auxiliary IC, with at least the auxiliary IC driving one or more MOS FETs to control supplying of power to respective electrical loads, e.g., in a vehicle. A stepped-up voltage, higher than the circuit power source voltage, is generated within the main IC and supplied to each auxiliary IC, for driving gate electrodes of the MOS FETs. Electrical noise produced by operation of a voltage step-up circuit in the main IC is effectively suppressed by elements that are coupled only to a power source terminal of the main IC alone.