A plurality of excitation elements are disposed on two facing sides of a quadrilateral detection range in a non-piezoelectric substrate, and a plurality of receiving elements are disposed on the other two sides of the detection range so as to face the excitation elements respectively. Surface acoustic waves are transmitted from the respective plurality of excitation elements in two diagonal directions of the detection range respectively, and the surface acoustic waves from the two diagonal directions are received by the respective receiving elements, so that a position of an object in contact with the substrate is detected based on received results in the receiving elements.