PURPOSE: To reduce the weight of an Oldham's ring as the sufficient compression resisting and stretch strength of the Oldham's ring is maintained and to reduce the generation of vibration and the generation of noise even during high speed operation.

CONSTITUTION: A fixed roll 12 and a moving roll 9 are engaged with each other with angles displaced from each other and with rotation of the moving roll 9 blocked by an Oldham's coupling 30, the moving scroll is caused to effect revolving movement based on the fixed scroll 12 and fluid is compressed or expanded. In which case, the Oldham's coupling 30 is structured in such a manner that first keys 21 and 22 engaged with key grooves 25 and 26 formed on the moving scroll 9 side are arranged on one surface side of the ring part 20 and second keys 23 and 24 engaged with key grooves 27 and 28 formed on the housing 1 side are formed on the other surface side. When rotation of the moving scroll 9 is blocked, the sectional area of a ring part on which a compression stress is applied is reduced to a value lower than the sectional area of a ring part on which a tension stress is exerted.