When a control valve allows communication through a fuel drain channel, fuel flows into an inner control chamber from an outer control chamber through a communication channel and flows out to a fuel tank. The fuel flow through the communication channel generates a differential pressure between inner control pressure and outer control pressure. Thus, an outer differential pressure immediately after an outer valve opening time can be set small, restraining an increase in the unburnt HC content of exhaust gas at low load, which could otherwise result from a high rising speed of an outer needle valve immediately after the outer valve opening time. An inner differential pressure immediately after an inner valve opening time can be set large, restraining an increase in the smoke content of exhaust gas, which could result from a low rising speed of an inner needle valve immediately after the inner valve opening time.