A reciprocating compressor comprising a cylinder block (3) having formed therein a plurality of cylinders (11), a shaft rotatably passing through the cylinder block and pistons engaged in reciprocating movement inside the cylinders (11) as the shaft rotates, which is installed by fastening mounting leg parts (31) disposed at the cylinder block (3) at mounting positions, is characterized in that the mounting leg parts are each constituted with a connecting portion (31a) extending from the cylinder block 3 and a projected portion (31b) formed continuously to the connecting portion to project on one side or both sides of the connecting portion along the tightening direction and that the projected portion (31b) has a lower level of rigidity compared to the connecting portion (31a). The reciprocating compressor eliminates the need for rigorous management of the piston clearance by assuring firm installation via the mounting leg parts and also assuring smooth movement of the pistons with the extent of cylinder deformation kept within the allowable range.