A burst wave is applied to an excitation element of a touch panel main body from an oscillation section so as to excite surface acoustic waves, and the excited surface acoustic waves are received by a receiving element of the touch panel main body. The received signals are A/D converted by a receiving section, and a control section calculates the contact position and the contact width of the object in contact with the touch panel main body, based on time-series changes in the received strength. Based on the received strength of surface acoustic waves, the control section controls the wave number of the burst wave to be applied to the excitation element.