PURPOSE: To improve the durability of a rubber bellows by utilizing the lubricating oil minutely leaked from the seal part of a mechanical seal.

CONSTITUTION: A horizontal open compressor has a mechanical seal M near the opening of a casing 1. On the front part of the mechanical seal M, an oil seal 9 for blocking an atmosphere open space, whose rear end part is blocked by a rubber bellows 7 and front end part is opened in the front of a fixed ring 5, is provided, and an oil reservoir space is formed between the rubber bellows 7 and the oil seal 9. The lubricating oil in the casing 1 leaked from the seal part of the mechanical seal is collected in the oil reservoir space to put the rubber bellows 7 in oil atmosphere.