PURPOSE: To dispense with a constant voltage circuit and high accuracy for the source voltage of an A/D converter and to improve coordinate detecting accuracy.

CONSTITUTION: This detector is equipped with first resistance film 101 and second resistance film 102 arranged confronting with each other, a power source supply means 103 which supplies potential to the first resistance film 101 or the second resistance film 102, a control means 104 which performs a first detecting operation which supplies power source potential Vs from the power source supply means 103 in the x-axial direction of the first resistance film 101 and detects coordinate potential VI from the second resistance film 102 when two sheets of film 101, 102 are brought into contact with each other at an arbitrary position P, and a second detecting operation which detects the source potential VS by switching arbitrarily, and an arithmetic means 105 which calculates the coordinate value xP of a contact point P from the x-axial potential VI and the source potential VS.