To provide a key input device where a user is not fallen into confusion upon an input.

The key input device includes: a light emitting part emitting the light of a selection color selected from a plurality of colors; a plurality of key tops transmitted through the light of the plurality of colors to be depressed by the user; a light guide part guiding the light of the selection color emitted by the light emitting part to each of the plurality of key tops; and a plurality of color filters provided correspondingly to of the plurality of colors, respectively, transmitted through only the light of the corresponding color of the light of the plurality of colors, disposed without overlapping a surface of each key top to be depressed by the user, and printed with characters of display formats divided in the plurality of colors on a surface.