A user interface device detects a fingertip placed on an imaging range. The imaging range is located or arranged so that a user inserts and place a hand along a predetermined direction. A device detects a tip area corresponding to the fingertip from the imaging range. The device determines whether the detected tip area is a finger or not. The determination can be performed by evaluating a size of the tip area, for example, whether the width is in an appropriate range or not. If the tip area is verified as a finger, a position of the fingertip is calculated. According to the device, it is possible to determine whether it is a finger or not by using a relatively simple algorithm. As a result, it is possible to eliminate objects other than finger and to provide sufficient accuracy for detecting the fingertip.