To provide an input device, allowing characters to be inputted by one hand and by a simple operation as an input device of an electronic apparatus, including a personal computer and a cellular phone, and to supplement a usable time of a secondary battery of an electronic apparatus, including a personal computer and a cellular telephone with a built-in electric generator.

A key event is transmitted to the electronic apparatus, including a personal computer, a cellular telephone and the like by turning a rotary key. In addition, the key event is transmitted to the electronic apparatus, including a personal computer, a cellular telephone and the like by depressing the rotary key. By these two operations, a simple and unified operation can be realized. The built-in electric generator is turned by turning the rotary key, and thereby generated power is supplied to the electronic apparatus, including a personal computer and a cellular phone and a secondary battery of the electronic apparatus, including a personal computer, a cellular phone and the like, and the usable time of the secondary battery is supplemented.