To provide a compressor preventing sticking of an O-ring of a shaft seal unit to a rotary shaft and ensuring sealing performance.

The shaft seal unit 40 for airtightly sealing the rotary shaft 30 to a drive side casing 22 has a fixed side seal member 90, which encloses the rotary shaft and maintains airtightness with the drive side casing, and a seal face 94 airtightly slided on the fixed side seal member, and includes a rotation side seal member 92 rotating together with the rotary shaft and the O-ring 98, which is engaged with the rotation side seal member and airtightly contacted with the rotary shaft by pressing force of a spring 102, wherein the rotary shaft has a shaft seal part 104 of a tapered shape which reduces tension acting on the O-ring and newly generates moving force of the O-ring.