PURPOSE: To provide the title control device which always faithfully corresponds to the contamination of air in a room by solving the trouble of resetting reference voltage at every use because the resistance value of a gas detection element at the time of purification changes with each day in the control unit of an air purifier for a car using a gas sensor.

CONSTITUTION: The saturation point of time of the temp. rise of a gas sensor at the ON-time of the switch of an air purifier is known by the temp. detection means 12 of the gas sensor and the output voltage of the gas sensor at this time is stored in a voltage memory means 13 as reference voltage and the output voltage of the gas sensor during the operation on and after and the reference voltage are subjected to comparative operation by an operation and control circuit 11 to operate the air purifier corresponding to the contamination of air.