An IC chip and a minute antenna for conducting transmission with a weak radio wave are mounted on a male connector. An auxiliary antenna for amplifying the weak radio wave emitted by the minute antenna and transmitting the amplified radio wave is mounted on a female connector. If the male connector is fitted into the female connector normally, then the distance between the minute antenna and the auxiliary antenna becomes 1.0 mm or less, and consequently the weak radio wave transmitted by the minute antenna is amplified by the auxiliary antenna and transmitted to the outside. Unless fitting is conducted normally, then the distance between the minute antenna and the auxiliary antenna becomes longer than 1.0 mm, and consequently the weak radio wave emitted the minute antenna is not amplified and transmitted. By receiving the information stored on the IC chip, the fitting state of the connectors can be checked.