PURPOSE: To obtain steam for heating foods, having proper humidity, by jetting high-pressure steam from a boiler from a specific nozzle into a tank, by adsorbing a heavy metal of antiscales on water, changing the high-pressure steam into low-pressure steam and separating excess water in a steam separating chamber.

CONSTITUTION: High-pressure steam from a boiler 1 is jetted from a specific nozzle 9 in a steam supply pipe 8 connected to the top of a tank 7 to which water is fed and a heavy metal, etc., of antiscales admixed during evaporation in the boiler 1 are adsorbed on water in the tank 7. Simultaneously the high- pressure steam jetted to the tank 7 is changed into low-pressure steam. Then the low-pressure steam is introduced to a steam separating chamber 34 equipped with a barrier plate 36 to obstruct the flow and excess water is separated by contact with the barrier plate 36 in the separating chamber 34. Then saturated steam having proper humidity at ≤110°C is fed to a food heating means 38.