A scroll compressor includes first and second scroll members housed in a casing. The first scroll member has a fluid inlet and a first through hole spaced from the fluid inlet. A fluid introducing pipe is configured to connect to the first through hole. A piston, having an annular groove and a second through hole, is disposed in the first through hole and is biased toward the fluid introducing pipe. The piston is configured to shut an end of the first through hole when fluid pressure larger than the biasing force is introduced into the fluid introducing pipe and to open the end of the first through hole when fluid pressure smaller than the biasing force is introduced into the fluid introducing pipe. A piston ring is fitted into the annular groove of the piston and has a stepped fitting end.