Each of multiple detection data values included in two-dimensional data, generated based on detection results of sensor unit, is converted into either an on data value or an off data value by a data conversion unit. Each data value included in the converted two-dimensional data is sequentially acquired from an edge of an operating face by a region identifying unit, and is determined whether an on data value or not. In a case where determination is made that the acquired data value is an on data value, the acquired data value is set as a starting point, and an outline of a set region where adjacent on data values form a set is tracked in order starting from the starting point until returning to the original starting point again.