The present invention intends to effectively utilize used superheated steam to suppress calorific loss as well as suppressing a heat quantity necessary to generate saturated steam from water in order to generate superheated steam. Also, the present invention includes: a superheated steam generating part 3; a steam supply flow path L1 for supplying saturated steam to the superheated steam generating part 3; a superheated steam utilization part 4 that is supplied with superheated steam generated by the superheated steam generating part 3; a steam return flow path L3 for returning used steam having passed through the superheated steam utilization part 4 to the superheated steam generating part 3; and a flowmeter 8 that measures a flow rate of the used steam returned to the superheated steam generating part 3, and on the basis of the difference between a desired flow rate of the superheated steam to be generated by the superheated steam generating part 3 and the flow rate of the used steam obtained by the flowmet
