An input device includes an input pen that is capable of detecting an amount of a pen pressure applied to a pen tip. The input pen has a resistance film that alters a resistance vale thereof according to a touch area, a spring that alters the touch area between the spring and the resistance film, a pen pressure detecting circuit that detects the amount of the pen pressure applied to the pen tip based on the touch area, and an infrared output circuit that outputs the amount of the pen pressure to a receiver with the use of infrared rays. The spiral-shaped spring is configured so that a diameter may become smaller as further from the pen tip. It is thus possible to detect the amount of the pen pressure applied to the pen tip based on the touch area that varies according to a movement of the pen tip, and thereby possible to express different line widths in drawing according to the amount of the pen pressure applied to the pen tip.
