PURPOSE: To provide a fitting device with a simple construction whose operation is not affected by the small size differential and deformation of flexible ringed parts and which is capable of considerably cutting down the required time for fitting.

CONSTITUTION: When flexible ringed parts such as seal rings 7 are fitted in the groove the 18a of work 18, a magazine tube 1 is placed on a magazine holder 2, and work 18 is set on the lower end section 17 of a rod 3. When air is supplied through a connector 15, a cylinder 11 is operated so that a push-out ring 8 made of a soft synthetic resin material is pushed out downward along the tapering surface of said rod 3 by a lowering movable plate 13. At this time, the lowermost one of said seal rings 7 fitted in said magazine tube 1 separates from said magazine tube 1 and is pushed down while increased in diameter. Said seal ring 7 having reached said lower end section 17 is fitted in said groove 18a with the bend section 8c of said push-out ring 8 bending downward.