PURPOSE: To perform an automatic forced operation and to enable a fast discharging operation to be carried out irrespective of the setting condition of an external switch when cigar smoke is detected.

CONSTITUTION: In a ventilation fan having a two-speed fan motor 2 capable of high or low operation within a main body 1 of the ventilation fan and an operating means utilizing a gas sensor 3 for detecting smoke and performing an automatic operation of the ventilation fan, if cigar smoke during smoking is detected, the operating means for performing the two-speed fan motor 2 under a fast operation even if the ventilation fan is set to have a low operation is provided.