PURPOSE: To simplify the structure of automotive coupling fan and reduce a manufacturing cost.

CONSTITUTION: A thermostat 20 has a metal bellows rotated along with the shaft 2 of a water pump. A filler vaporizing in a prescribed temperature range is filled in the metal bellows of the thermostat 20. When the temperature of a cooling water is low, the metal bellows is not deformed due to no vaporization of the filler. When the temperature of the cooling water is high, the filler is vaporized and the metal bellows is deformed by the vaporized pressure and a rod 19 moves in the axial direction and a friction disk 21 is engaged with a matched friction disk 22 and the fan is rotated. When the temperature of the cooling water is lowered, the vaporized pressure is lowered and the thermostat 20 is returned to the origin and the fan is stopped.