A scroll compressor comprises two scroll members, each of which has an end plate and a wrap formed on the end plate so as to extend perpendicularly therefrom, are meshed with each other, one scroll member being orbited with respect to the other without being self-revolved, to introduce a gas into working chamber. The working chamber is formed by these two scroll members, compresses the gas therein and then discharge the same to the outside. A seal mechanism for pressure-sealing between the working chamber or the suction side and a space on a rear surface of the orbiting scroll member is provided on the same rear surface, and also a pair of small-diameter ports for communicating the mentioned space and working chamber with each other are provided on the end plate of the above-mentioned scroll member, whereby the outer diameter of the scroll members can be minimized, and the axial opposed end surfaces of the two scroll members can be maintained in sealed condition.