PURPOSE: To prevent an erroneous input caused by contact of a foreign matter, etc. by sensing a temperature of the human body by plural thermocouples provided on the X - Y coordinate input device of a touch panel system, and converting it to an electric signal.

CONSTITUTION: When the human body or a fingertip comes into contact with a transparent plate 1, only a thermocouple with which the fingertip comes into contact in thermocouples 2 integrated like a lattice into the transparent plate 1 is subjected to temperature variation by the body heat. As a result, a potential difference is generated in the thermocouple 2, and inputted to a transducer 3. The transducer 3 executes comparison with a potential difference of other thermocouple 4 with which the human body does not come into contact, and simultaneously, a variation rate of the potential difference is calculated, and in the case the variation rate is small, it is not recognized as input data. The input data recognized by the transucer 3 is inputted to a coordinate data converting circuit 5. By the coordinate data converting circuit 5, a coordinate of the thermocouple 2 in which the potential difference is varied is calculated, and outputted to a system bus 7.