To provide an inverter parallel operating system and its controller IC by which a plurality of inverters to drive a plurality of loads needing a high voltages such as a CCFL are disposed near each load, and are synchronously controlled at the same phase.

Each inverter is disposed near a plurality of the loads needing the high voltage, and an oscillator block is provided that determines oscillating operation or nonoperation depending upon whether a resistor to determine a frequency is connected to each inverter or not, by which each load is synchronously controlled at the same phase with one inverter as a main and the other as a subinverter. Moreover, at starting, a resistance value of the resistor to determine the frequency is set substantially lower while the frequency is set higher, then a plurality of the loads early start up.