Abstract: In order to provide an integral whole unit for continuously measuring the quantity of heat needed to melt snow lying on a road, and prevent freezing of the road; and for controlling a supply of heat to the road for melting the snow lying on the road and for preventing the freezing of the road, it uses a road-simulated device. The road-simulated device is put outdoors while it is snowing, and it is heated and kept at a temperature of -0.degree. C., thus keeping the road-simulated surface free of snows, and preventing the freezing of the road-simulated surface. In this condition the thermal energy required to keep the simulated road surface unfrozen is determined, and every control variable is determined on the basis of this so determined thermal energy.