PURPOSE: To easily notice users of closer life expectancy of parts made of rubber or synthetic resin, which are now being used, by means of the breakage of a ring or the dropping of the ring due to the breakage thereof by mounting a ring whose rate of degradation is faster than the life expectancy of parts, directly on the parts, the life expectancy of which is to be predicted, or by mounting the ring indirectly on a point which is considered to be of the same environment as that of the parts.

CONSTITUTION: A ring 1 is formed smaller than the outer diameter of parts, the life expectancy of which is to be indicated, by a material, the degradation of which due to environment is faster than the parts which are made of rubber, synthetic resin or metal and the like. A notched part 2 is provided on one or more parts of the ring 1, or the cross section of the ring is reduced in one or more parts of the ring 1.