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