Abstract: A reciprocating compressor is provided with a plurality of gas compression means having a cylinder and a piston, the piston of each gas compression means is cooperated with the compressor by converting a rotating motion of a crankshaft provided on an electric drive source to a reciprocating motion by a scotch yoke mechanism, wherein an increase of the volume of discharged gas can be achieved without designing a gas compression means to be wide or without increasing the number thereof, a pulsation of discharged gas can be decreased by an attachment of an expansion muffler on the cylinder head so as to decrease a vibration and noise of the compressor, an attachment of the fly wheel to the crankshaft and an adjustment of the shaft with the crankshaft can be improved easily, further compressed gas flows are joined and discharged in concentration, thereby the pulsation of discharged gas can be restrained.