PURPOSE: To provide a stirring engine, which can control the pressure of a working space reliably with sufficient control width to control the output, without making an engine as a system large.

CONSTITUTION: Working fluid is sealed in a crank chamber 6 of an engine, and the crank chamber 6 and a working space are connected by a pipeline comprising a pair of check valves 10, 11, which are connected in backward parallel with each other, and a pair of solenoid valves 12, 13, which are connected in series to these check valves 10, 11. The described solenoid valves 12, 13 are controlled in response to the desired pressure of the working space.