A hermetic compressor includes a plurality of compressing mechanisms. Each of the compressing mechanism includes a rotary cylinder having a groove, and a piston slidable in the groove, so that a compressing stroke is carried out by rotation of said piston on a locus of a radius E about a point spaced apart at a distance E from the center of said rotary cylinder. A partition plate is interposed between the rotary cylinders of the adjacent compressing mechanisms. The partition plate is provided with a communication bore through which a shaft is passed. The partition plate is provided with cranks on which said pistons can be mounted. A motor mechanism section is adapted to drive the pistons of the compressing mechanisms by the common shaft. At least one of the compressing mechanisms is different in phase in a compressing stroke from the other compressing mechanisms. The rotary cylinders of the adjacent compressing mechanisms and said partition plate sandwiched between such rotary cylinders are formed from different members, and relatively non-rotatably connected to each other. Thus, the piston rotated in the above manner about the above-described point is not necessarily requited to be rotated about its axis during the rotating movement about such point, and need be only slid along the groove. Therefore, the piston can be formed into a non-circular shape, whereby the area of contact of the piston with the groove can be increased to enhance the sealability, thereby enhancing the suction and compression efficiency.