A wireless tag adapted for mounting inside a hollow electrically conductive pipe, includes: a contact placed in contact with the electrically conductive pipe so as to be electrically connected to the electrically conductive pipe; a lead wire placed inside the electrically conductive pipe along a longitudinal direction of the electrically conductive pipe and spaced a prescribed distance away from an inside wall of the electrically conductive pipe, thereby forming a coaxial line together with the electrically conductive pipe; and a wireless tag circuit, electrically connected at one end to the contact and at the other end to the lead wire, for generating a response signal in response to an interrogation signal transmitted from a reader/writer.