READER/WRITER

PROBLEM TO BE SOLVED: To communicate with a data carrier of a plurality of standards with different antenna constants and to always secure normal communication even to a fluctuation in communication distance between the data carrier and a reader/writer. SOLUTION: In this reader/writer 1, a CPU 3 always controls the output voltage of a D/A converter 15 to always change reference voltage G until receiving a response packet, i.e., until reception start timing. When the response packet is received, the reference voltage G is changed in a similar manner during start of frame, an operation point where normal continuous data are read in an input-output port 6 in the reference voltage G that is changed, that is, voltage to be an operation point where a normal binary signal H is obtained as a result of a normal operation of a binarization circuit 12 is recognized, and the CPU 3 fixes a D/A converter input signal J being an output of a latch 14 and sets output voltage of the D/A converter 15 to the voltage. COPYRIGHT: (C)2005,JPO&NCIPI