To provide a key input device capable of minimizing the deterioration of operability or reduction in input speed in a general input operation and preventing generation of sound in an input operation while sound cannot be generated because the circumference is calm by enabling the switching of input mode according to the circumferential state.

In the key input device 3 having a push button key 2, a touch sensor 4 is provided on the surface of the key 2. According to this, either a push button input mode capable of inputting when the key 2 is pressed or a touch button input mode capable of inputting when the touch sensor 4 on the surface of the key 2 is touched can be selected by the operation of a mode change-over switch 8.