A rocking piston type compressor is provided with a piston rod, a lip ring, and a ring holding member. The lip ring includes a center portion fixed by the ring holding member, and a lip portion upwardly extending around the center portion along a periphery of the ring holding member. The ring holding member includes a flange portion covering at least a part of an upper end surface of lip portion. A back pressure introducing portion is provided in a part of the flange portion.