A heater control unit controls electric power supplied to a heater provided in a seat. The heater control unit includes an outside air temperature measuring portion that measures an outside air temperature, a seat surface temperature measuring portion that measures a surface temperature of the seat, and a control portion. The control portion controls a time for which an initial electric power larger than an electric power in a steady state after the initial state is output to the heater, according to the measured outside air temperature and the measured seat surface temperature in an initial state immediately after the heater is activated.