PURPOSE: To prevent the vibration of the axis of a rotary piston in the primary space and improve the noise insulation effect by forming a discharge path so that the pressure wave from a discharge port on one side of a muffler and the pressure wave from a discharge port on the other side negate together.

CONSTITUTION: Side covers 13a, 13b are provided on both sides of a cylinder 11 eccentrically provided with a rotary piston 12, a compression chamber 19 is formed by a blade 15 in the cylinder 11, a discharge path 17 is formed on one side cover 13a, and one end of it is formed with a pair of the first discharge ports 42 opened on the primary space 21 side in the casing 2. The discharge ports 42 are provided at symmetrical positions with respect to the perpendicular line to the axis 5. The other end of the discharge path 17 is formed with the second discharge port 44 opened on the cylinder 11 side, and the discharge port 44 is provided on the perpendicular line. The first discharge ports 42 are opened in a muffler 46 and opened or closed by a discharge valve 41.