Threshold values smaller than degrees of proximity of an object indicated by detection data at peak positions are set based on detection data of the peak positions at which a degree of proximity of the object is higher than that of surrounding detection positions. An evaluation value according to an area of a region on a detection surface occupied by a group of detection positions, including the peak positions, in which degrees of proximity of the object indicated by detection data are higher than the threshold values, is calculated, and it is determined whether the object in proximity to the peak position is a finger or a palm based on the evaluation value.