PURPOSE: To promote the simplification of a structure in an exhaust pressure regulating mechanism of a rotating rotor device, by providing an opening within the range of a compression stroke in a casing further a passage, which communicates with a compressing action chamber and a delivery pipe through the opening, while an opening and closing means in the passage.

CONSTITUTION: A rotating rotor device 1 has both inner and outer rotors 3, 4 in a casing 2, further both the inner and outer rotors 3, 4 rotate in an equal angular speed in the periphery of the respective rotary axes 5, 6. While the casing 2 provides a suction port 7 and a delivery port 8. In the above constitution, an opening 9 is provided in the casing 2 within its range of a rotary angle of a compressing action chamber 12 in accordance with a compression stroke by rotation of both the inner and outer rotors 3, 4. While a passage 10a, which communicates with a delivery pipe 11 and the compressing action chamber 12 through the opening 9, is opened to the casing 2. And a valve means 13, comprising a valve 15 sliding in the passage 10a so as to open and close it and a spring 16 pressing the valve 15 to a side of the opening 9, is provided in the passage 10a.