A heater is installed indoors and heated to a target temperature. The heater is controlled by a controller. The controller has a regular control module which heats the heater to reach the target temperature. In addition, the controller has a suppressive control module which heats the heater to a suppressed temperature lower than the target temperature by electric power suppressed so that surface moisture adhering on the surface of the heater is decreased. When an activation of the heater is ordered, the heater is heated by the suppressive control module, after that, the heater is heated by the regular control module. The surface moisture is decreased by the suppressed temperature. Therefore, generating rapid boiling and/or rapid evaporation of the surface moisture by the target temperature may be suppressed.