Depletion-mode ferroelectric transistors are adapted for use as non-volatile memory cells. One end of an ink supply tube 910 is inserted through the holes of the wall faces 1a, 370w1, and 370w2 and is connected with an inlet 401 of a vertical communicating path 400 located in the upstream of a sensor unit 30 functioning as a detector. The connection is achieved by relying on bolts used to attach a hub cap to the axle, without eliminating the hub cap, and at the same time providing a sturdy and robust connection capable of withstanding forces expected to be applied to a wheel cover during its lifetime. Upon receiving the repeat request on the sender, the data packet is resent from the sender to the receiver.