A scroll type compressor comprises a housing and a fixed scroll. A movable scroll is incorporated therebetween, eccentrically engaging with the fixed scroll, and has a rotating center and a revolving center. Pin members are arranged on the end plate of the movable scroll and on the housing. At least one of the pin members of the movable scroll is positioned on a first line and disposed downstream of the corresponding pin member of the housing in the rotating direction, when the volume ratio of a compression chamber is from 10 to 22 percent of the volume of the compression chamber at the time of the conclusion of the suction of medium. The first line passes through the rotating center and is perpendicular to a second line, which passes through the rotating and revolving centers. The compressor also has annular ring members, which contact at least a pair of the pin members of the movable scroll and the housing, to prevent the movable scroll from rotating.