PURPOSE: To avoid actuation failure of a piston and a compressor caused by spill of oil by forming annular shield elements for capturing leaking oil and exhausting it to an exhaust port in a cylinder facing a space between a guide portion and a work portion of the piston.

CONSTITUTION: A crankshaft 2 supported in a crankcase 1 is connected to a piston 6 contained in a cylinder 7 via a rod 4. The piston 6 is provided with a guide portion 6a and a work portion 6b. An oil wiper device 20 is disposed in the guide potion 6a, and a leakage exhaust port 22 is formed in the work portion 6b. In this compressor, a suitable number of annular shielding elements 31 for capturing leaking oil are formed in the cylinder 7. Then, the annular shielding elements 31 are affixed between motion regions of the guide portion 6a and the work portion 6b, and surround the piston 6 so as to shield a dry cylinder portion 7b from the guide portion 6a.