A touch panel device includes a touch panel unit, a fingerprint image capturing unit, a size derivation unit, and a control unit. The touch panel unit includes a display section that displays information about an operating instruction for a user. The touch panel unit detects the condition of contact with a user's finger to accept an input of the operating instruction. When the touch panel unit is pressed by the user's finger, the fingerprint image capturing unit captures an image of a fingerprint of the user's finger pressing the touch panel unit. The size derivation unit derives a size of the user's finger having pressed the touch panel unit from the fingerprint image captured by the fingerprint image capturing unit. The control unit controls the operating instruction based on the size of the user's finger derived by the size derivation unit.