Patent ID: 7423518

Claim:
A reader/writer performing a two-way communication with a contactless tag through electromagnetic induction and supplying electric power to the contactless tag, comprising: a plurality of antenna circuits, each of the plurality of antenna circuits having a first antenna coil for electromagnetically coupling with a second antenna coil in the contactless tag; a first amplifier circuit amplifying a signal which each of the plurality of antenna circuits transmits; a plurality of first switches, each of the plurality of first switches provided between the first amplifier circuit and each antenna circuit; a second amplifier circuit amplifying a signal which each of the plurality of antenna circuits receives; a plurality of second switches, each of the plurality of second switches provided between the second amplifier circuit and each of the plurality of antenna circuits; a control circuit turning on a predetermined switch among the first switches and a predetermined switch among the second switches, wherein the first antenna coils have a loop shape and a plurality of the first antenna coils are provided adjacent to each other in the same plane, and the loop of the first antenna coils has a shape such that an adjoining region of the first antenna coils becomes as small as possible.