To accurately estimate the remaining life times of solid insulators for power receiving and distributing equipment of which the insulators deteriorate due to the combined influences of a plurality of deterioration factors.

The following items are taken as evaluation items: the amount of various ions, including nitrate ion, sulfate ion, chlorine ion, and calcium ion, sticking to a new solid insulator for power receiving and distributing equipment and a solid insulator for power receiving and distributing equipment as a specimen; and the colors of both the solid insulators for power receiving and distributing equipment in a color specification mode b. These evaluation items are used comprehensively, to represent the degree of insulator deterioration with a single index. The remaining lifetime of the solid insulator for power receiving and distributing equipment as a specimen is estimated, based on the relation between the operating time and the index which has been determined beforehand.