An idle control system applicable to a fuel cell vehicle 1 is provided for improving the fuel efficiency. When the fuel cell vehicle is determined to be in a predetermined idle mode, the idle control system stops a compressor to thereby stop power generation of a fuel cell. In contrast, when the state of charge of the capacitor 4 falls below a predetermined value while the fuel cell vehicle is in the idle mode, the idle control system drives the compressor 8 by means of the capacitor to drive the fuel cell in order to charge the capacitor.