PURPOSE: To prevent the cold draft due to a low electric power by a method wherein an electric power supply to a heater is controlled in accordance with a temperature difference between a surface temperature, detected by a detector detecting the surface temperature of a wall body, and a room temperature detected by a room temperature detector.

CONSTITUTION: In a heater unit 4, a heater is arranged so as to keep a proper distance from the wall body of a window surface or the like while the surface temperature of said wall body is detected by a surface temperature detector 5. The room temperature is detected by the room temperature detector 6 and a control unit 7 controls the electric power supplied to the heater in accordance with a temperature difference between the surface temperature, detected by the detector 5, and the room temperature, detected by the detector 6. The heater is conducted only when the cold draft is generated and when the cold draft is generated, the direction of the draft is changed by an ascending airstream generated at the inner side of the room than a descending airstream due to the cold draft to prevent the cold draft from invading into a living area. Accordingly, an electric power consumption may be less than the same of conventional heating unit.