PURPOSE: To prevent excessive compression of gas and an increase of its input, by providing a subdelivery hole, equipped with a check valve, in the prescribed position of a cylinder determined by a contact point, suction port in the leading side, delivery port, etc.

CONSTITUTION: A subdelivery port 10 with a check valve 9 is opened to a cylinder 1 in the range of an angle θ in a relation, where max (θs+2π/n, θd-2π/n)< θ<θd, when assuming θs for suction angle, formed from a contact point P to an end point 2a of a suction port 2 in the leading side, θd for delivery angle, formed from the contact point P to a start point 3a of a delivery port 3 in the leading side, and (n) for number of sheets of vanes. A vane 5, if it is actuated from the first period of a delivery stroke positioning before and behind and interposing the port 10 to the latter period turning a rotor 4, compresses gas in a compression chamber 8 to a delivery pressure. In this way, the check valve 9 is opened, delivering refrigerating gas, and its excessive compression is prevented.