To provide a steam ejector device which reduces a fluctuation in steam pressure supplied from a delivery pipe.

A high pressure driving steam pipe 3 and a low pressure suction steam pipe 4 are respectively connected to a suction chamber 1 of a steam ejector 10. A pressure regulating valve 5 is installed in the driving steam pipe 3. A diffuser 2 is connected to the delivery pipe 6. A pressure sensor 7 is installed in the delivery pipe 6. A bypass passage 11 is arranged in parallel to the steam ejector 10, and a pressure reducing valve 12 is installed as a pressure control valve. When the delivery pipe 6 side steam pressure reduces up to a prescribed value, the pressure reducing valve 12 automatically opens, and supplies high pressure steam in the delivery pipe 6 from the driving steam pipe 3 so that the delivery pipe 6 side steam pressure is maintained in a prescribed range.