An idling state stabilizing device for an engine is disclosed that can decrease the torque that is necessary for rotation of a magneto by decreasing an output current, without setting an engine speed high, even though the engine is in the idling state, can stabilize the engine rotation, and accordingly can improve fuel economy, and further can reduce noises. A current value output from a generator when an engine is in an idling state is set as an output current value in a power generation control device. The power generation control device determines that the engine is in the idling state when the engine speed becomes equal to or less than an idling state rotational speed, detects the maximum engine speed and the minimum engine speed during a predetermined time period when the engine is in the idling state, calculates an engine speed fluctuation amount of the engine by subtracting the minimum engine speed from the maximum engine speed, and controls the current value output from the generator to be a low output current value which is lower than the previous output current value when the engine speed fluctuation amount is equal to or greater than a predetermined amount.