PURPOSE: To correctly detect the value information of a card by reading the time value at every changing point of a signal from an inserted card, and determining the central value of all the read-out time values, and determining magnitude relation with the central value for all the time values, and judging either a first or a second value in accordance with this determined magnitude relation.

CONSTITUTION: A control part 31 to control a card reader/writer device is connected to a control unit 30 being a host device through a transmission/ reception circuit 32. Date is recorded in the card as the binary data of a first value whose signal level changes once at every prescribed time and a second value whose signal level changes twice at every prescribed time, and the binary data of the card is reproduced, and the first or the second value is judged. Here, the time value at every changing point of the signal is read successively from the inserted card, and the central value of all the read-out time values is determined, and simultaneously, the magnitude relation with the central value is determined for all the time values, and either the first or the second value is judged in accordance with this determined magnitude relation.