To achieve a higher precision in temperature control of the hot air injected out of a hot air mat.

A hot air injection pipe 2 with hot air injection ports 3 is installed in the hot air mat 1 such as a bedding and the air blown from a fan 16 is heated with a heater 18 and the heated air is guided with an hot air hose 5 to the hot air injection pipe 2 to be injected out of the hot air injection ports 3. A controller 10 loads the atmospheric air temperature Te detected with an atmospheric air temperature detection sensor 21, the temperature Th of the hot air delivered from the heater after heating with the heater as detected with a heater delivery hot air temperature sensor 20 and the hot air injection temperature Tdet detected with a hot air injection temperature sensor 22 to compute the heater off temperature Tof of the heater 18 using the expression with the Te and the set hot air temperature Tst as variables. When the detected temperature of the hot air with the heater delivery hot air temperature sensor 20 reaches the heater off temperature Tof, the controller 10 turns off the heater 18 or turns it on when the heater delivery hot air temperature sensor 20 or the hot air injection temperature sensor 22 detects the heater on temperature.