To provide a rotary gas compressor for more surely preventing the oozing-out of lubricating oil along a rotating shaft in the outward direction of a housing.

The rotary gas compressor 10 comprises a compression mechanism 12 which has a rotor 23 for compressing gas taken out of a low pressure space 29 and to which the lubricating oil is supplied, and the housing 11 housing the compression mechanism 12. The rotor 23 has the rotating shaft 18 to which rotating power is transmitted from the outward direction of the housing 11. In the housing 11, a bearing 24 is provided for allowing the pass-through of the rotating shaft 18 and bearing it. A mechanical seal mechanism 50 is provided between the bearing 24 and the rotating shaft 18. In the housing 11, an oil collection space 61 is provided encircling the rotating shaft 18 on the opposite side to the compression mechanism 12 in view from the mechanical seal mechanism 50. In the oil collection space, a secondary seal means is provided encircling the rotating shaft 18. In the housing 11, an oil return passage is provided for communicating the oil collection space with the low pressure space 29.