To easily fasten a seal member to an annular body by bonding the seal member in which adhesives are applied to the inner peripheral surface of the annular body, and easily attaching a seal member mounting jig.
A seal member mounting jig to be used when an annular seal member is mounted on the inner peripheral surface of an annular body is composed of a main pressing plate 11 having the length shorter than that of the inner periphery of the annular body, an auxiliary pressing plate 12 attached to the inner surface central part, and a pressing device 13. The pressing device 13 is composed of a receiving table 16, a pressing member 17 facing it, an operating handle 18, and a pressing force applying means 21. The pressing member 17 is attached to the receiving table 16 so as to be freely oscillated in relation to the receiving table 16 by the operation of the handle 18, the pressing force applying means 21 is provided between the receiving table 16 and the pressing member 17 or the handle 18, the receiving table of the pressing device 13 is attached to the inner surface of the intermediate part of the auxiliary pressing plate 21, and the receiving table 16, the auxiliary pressing plate 12 and the main pressing plate 11 are integrated with one another.