Provided is a touch-panel device capable of detecting a touched position with high accuracy even when a touched area extends off an electrode area. In one embodiment, the touched area is assumed to be, for example, circular in shape. A width in an X direction (overlap width) and a width in a Y direction (overlap width) of an overlap area where the touched area in a circular shape and an electrode area overlap each other is determined based on sensor measured values. When the overlap width and the overlap width are different from each other, it is judged that the touched area extends off the electrode area, and a position of a center of the touched area in the circular shape is calculated as the touched position.