<p>A seal structure adapted for use between a rear head (38) having a discharge port for discharging a compressed refrigerant and a rear muffler (39) placed so that a muffler space (A2) is formed between the rear muffler (39) and the rear head (38). The rear head (38) has a body (38b) having a shaft receiving hole (38a) into which a shaft is inserted, an annular boss (38c) projecting from the body (38b) so as to surround the shaft receiving hole (38a), and an annular side wall (38d) projecting from the body (38b) so as to surround the boss (38c). The rear muffler (39) has an opening (39b) into which the shaft is inserted and is fastened to the head end surface of the side wall (38d) such that the peripheral edge (39c) of the opening (39b) is in contact with the head end surface of the boss (38c). The head end surface (38g) of the boss (38c) has, on its entire periphery, a portion located on the opposite side of the body (38b) from the position of a surface including the head end surface (38h) of the side wall (38d).</p>
