Temperature measurement data obtained by measuring the temperature of a cable clamp (31) by a temperature sensor (320) is radio-transmitted from a temperature sensing unit (32) at a predetermined timing, and the radio-transmitted temperature measurement data is received by a receiving station (5), classified by the temperature sensing unit number, and stored in a temperature measurement data storage area (502A). The temperature measurement data transmitted from twelve temperature sensing units (32) can be received by one receiving station (5).