PURPOSE: To save energy for preheating power by using outdoor brightness as data for setting heating conditions when heating road surface using various data to make show melting, icing prevention, etc.

CONSTITUTION: In addition to conventional detections of paved body temperature, road surface moisture, ambient temperature, presence or absence of snow removal, etc., the outdoor brightness is detected using a pyrheliometer 1, etc. Next a controller main body 10 turns on and off a switching element 11 based on these detected values to turn on and off a power supplied from a power 12 to a road surface heating heater 13. Then, because snow fall probability is low when it is fine and bright even if ambient temperature is low, the paved body temperature in preheating operation in daylight is set lower. For hot water type heating system, also hot water supply is turned on and off controllably in the same manner. Thus, even if preheating temperature is lowered remarkably, snow melting capacity at the initial period of snow fall can be maintained, and also energy for preheating can be saved.