To provide a sorting method for restraining accumulation probability, where an operating voltage V is within a standard voltage range, to less than a predetermined reference accumulation probability even if an isolation valve 44 is reused in a next second period W2 in the isolation valves 44 for gas meters used in a first period W1.

A control voltage is given from a control means 45 to the isolation valve 44 for stopping when an abnormal state is detected by a pressure switch 21. The isolation valve 44 that is equal to or more than a predetermined sorting voltage V2Las or less than V2Has is selected for reuse from the operating voltage V1 of the total number (N) of isolation valves used in the first period W1. For setting the sorting voltage, the isolation valve after using for the first period W1 is subjected to an accelerated degrading test for the second period W2, and the operating voltage V2 is measured. Accumulation probability, where the operating voltage V2 is within a specific voltage range, is measured for each sorting voltage in a plurality of types. A set voltage that is less than the first accumulation probability and corresponds to a value closest to the first accumulation probability is set as the sorting voltage in the accumulation probability.