PURPOSE: To prevent a flow of air from rapidly changing, by electrically connecting a mode instruction means, which operates outputting an operation mode signal when a room temperature decreases to a preset value or less during time limit driving by a timer means, with a driving control means and the timer means.

CONSTITUTION: A motor fan, during its time limit driving by a timer means 19, detects a room temperature by a room temperature detecting means 10 to be compared with a preset value preset by a setting temperature variable knob (not shown in the drawing) in a temperature comparator circuit 13. And the circuit 13, when the room temperature decreases to the preset value or less, outputs a compared signal to an operation mode switching circuit 15 in the next stage. The circuit 15, outputting an intermittent operation signal to a fan motor driving circuit 17 by said compared signal and an intermittent mode signal output from an intermittent operation circuit 20a, interruptedly rotates a motor 2. Accordingly, the motor fan, causing no rapid change of a flow of air and performing again coupling operation is thereafter the room temperature increases to the preset value or more, stops operation if a preset time passes by repeating the above action within the preset time. In this way, the rapid change of a flow of air can be eliminated.