PURPOSE: To reduce the capacity of a steam supplying device to be used and to device economical use adopting a system to give priority to steam supply to a heater in the case of simultaneous operation of a heating device and a warming device.

CONSTITUTION: The steam generated in a boiler 1 is sent through a steam piping 2 to the heating device 3 or the warming device 4 and is used for heating and warming food. A controller 6 detects the temp. by a temp. detector 5 disposed in the warming device 4 and opens a steam control valve 7B when the temp. falls down to a steam supply temp. in the case of execution of warming. The controller so controls that a specified temp. is maintained by supplying the steam to the warming device. Thus controller 6 opens a steam control valve 7A and executes the steam supply during the lapse of the set time to the heating device in the case of execution of heating. The steam supply to the warming device 4 is not executed and the priority is given to the steam supply to the heating device 3 even if the temp. of the warming device 4 falls down to the steam supply temp. in the case of execution of the heating during working of the warming device 4. The heat supply to the warming device 4 is then executed after the end of the heating.