PURPOSE: To confirm mounting error without fail by providing at least one flow passage in a packing part.

CONSTITUTION: A packing part 4 becomes thicker in the direction of a free end 4a, is provided with a rib 12, and is provided with a groove 9 on an outer face 8 and an end face 13 and a ring part 15 in a face in the radial direction. Here, a deformed part 16 forming rising parts 17, 17' extending in a waveform or in a meandering manner in the peripheral direction and a recessed part 18 between them is provided in the ring part 15. At the time of sealing test, when the packing part 4 is folded back and the outer face 8 comes into contact with a shaft, the recessed part 18 forms a flow passage in which compressed air flows. Consequently, it is possible to confirm mounting error of a packing ring without fail.