PURPOSE: To improve the catalytic effect and reduce the power consumption, in the use of a plurality of ceramic heater-elements of negative characteristic provided with a noble-metal catalyst having the deodorizing function, by controlling a blower in such a manner as to reduce its air volume when the heater-elements are connected in series.

CONSTITUTION: When a changeover switch CSW and a main switch MSW are closed, the operation of a blower 5 is shifted to 'strong' for a large volume of air and ceramic heater-elements 1a, 1b of negative characteristic 1a, 1b are connected in parallel. Given 20Ω as the resistance of each of the heater-elements 1a, 1b, the power consumption, simply calculated from the combined resistance of 10Ω, comes to 1,000W. When the changeover switch CSW is opened, the blower 5 is shifted to 'weak' for a small volume of air, the heater-elements 1a, 1b are connected in series, and the combined resistance comes to 40Ω and the power consumption to 250W; nevertheless, with a ceramic of negative characteristic in use for the heater-elements, the heater can keep the temperature unaffected or even raises it higher for the reduced power consumption depending on the air volume of the blower, the device in size, and the like. Therefore, even for a small volume of air the temperature of a noble-metal catalyst can be raised, and for the small power consumption the catalysic effect makes it possible to improve the efficiency with which indoor air is cleaned.