A mobile terminal, comprising: a terminal body; and an input device (200, 300) mounted on the terminal body, wherein the input device comprises: at least one key button (210, 310) formed of a transparent material and having an internal space; an illumination sensor (220, 320) located in the internal space and having a light-receiving portion (221, 321), the illumination sensor (220, 320) configured to sense ambient illumination of the terminal body; a light-emitting portion (230, 330) located at a side of the illumination sensor (220, 320) and configured to output a light signal to the outside of the key button (210, 310) for detecting a touch applied to the at least one key button (210, 310); an input signal generation unit configured to generate a touch input signal according to the light signal input to the light-receiving portion of the illumination sensor (220, 320); and a spacer with an elastically deformable material between the illumination sensor (220, 320) and an internal wall of the at least one key button (210, 210), wherein a through hole is formed at the spacer for inputting a light signal to the light-receiving portion (221, 321) of the illumination sensor (220, 320). a terminal body; and an input device (200, 300) mounted on the terminal body, wherein the input device comprises: at least one key button (210, 310) formed of a transparent material and having an internal space; an illumination sensor (220, 320) located in the internal space and having a light-receiving portion (221, 321), the illumination sensor (220, 320) configured to sense ambient illumination of the terminal body; a light-emitting portion (230, 330) located at a side of the illumination sensor (220, 320) and configured to output a light signal to the outside of the key button (210, 310) for detecting a touch applied to the at least one key button (210, 310); an input signal generation unit configured to generate a touch input signal according to the light signal input to the light-receiving portion of the illumination sensor (220, 320); and a spacer with an elastically deformable material between the illumination sensor (220, 320) and an internal wall of the at least one key button (210, 210), wherein a through hole is formed at the spacer for inputting a light signal to the light-receiving portion (221, 321) of the illumination sensor (220, 320). at least one key button (210, 310) formed of a transparent material and having an internal space; an illumination sensor (220, 320) located in the internal space and having a light-receiving portion (221, 321), the illumination sensor (220, 320) configured to sense ambient illumination of the terminal body; a light-emitting portion (230, 330) located at a side of the illumination sensor (220, 320) and configured to output a light signal to the outside of the key button (210, 310) for detecting a touch applied to the at least one key button (210, 310); an input signal generation unit configured to generate a touch input signal according to the light signal input to the light-receiving portion of the illumination sensor (220, 320); and a spacer with an elastically deformable material between the illumination sensor (220, 320) and an internal wall of the at least one key button (210, 210), wherein a through hole is formed at the spacer for inputting a light signal to the light-receiving portion (221, 321) of the illumination sensor (220, 320).