A scroll fluid machine that suppresses fluctuations in a port aperture area during each revolution of an orbiting scroll. Suction ports for sucking in a working fluid are disposed on a second base plate to have openings in a vicinity of a winding start end portion of a second spiral tooth, and near an inward facing surface of the second spiral tooth at a position separated by an involute angle approximately 90° from the winding start end portion of the second spiral tooth. Discharge ports for discharging the working fluid are disposed on a first base plate to have openings in a vicinity of a winding start end portion of a first spiral tooth, and near an inward facing surface of the first spiral tooth at a position separated by an involute angle approximately 90° from the winding start end portion of the first spiral tooth.