To provide a steam heating device having a simplified structure by dispensing with a plurality of valves as switching units.

A jacket portion 25 of a reaction vessel 20 is connected to a positive-pressure fluid force-feeding unit 36 and an ejector vacuum pump 24 through a negative pressure/positive pressure changeover valve 22. The negative pressure/positive pressure changeover valve 22 includes a fluid inlet 2, a negative-pressure fluid outlet 4, and a positive-pressure fluid outlet 5. When a negative-pressure fluid inflows through the fluid inlet 2, it is discharged to the ejector vacuum pump 24 through the negative-pressure fluid outlet 4. On the other hand, when a positive-pressure fluid inflows through the fluid inlet 2, it is discharged to the positive-pressure fluid force-feeding unit 36 through the positive-pressure fluid outlet 5.