To provide an idling stabilizing device for a vehicle which can effectively prevent an engine speed from being rapidly lowered or the engine from being stopped even if an excessive electric load is applied to an alternator.

This stabilizing device has a variable speed engine output transmitting means for transmitting the rotation of an engine to an alternator 7 in addition to the control of an ordinary auxiliary intake valve 1 (crankshaft pulley 4, belt 12 and alternator pulley 8) and an alternator pulley control unit 6 for controlling the variable speed engine output transmitting means and, when an excessive electric load is applied to the alternator 7, it controls a rapid change in a load applied to the engine by changing the above described variable speed whereby prevents the engine speed from being rapidly lowered or the engine from being stopped.