The invention provides a key input device comprising a plurality of key tops 7 arranged on a surface of a main body case, each of the key tops 7 having a body 73 of transparent resin, the key body 73 being provided with a light blocking film 71 formed over a front surface thereof, the light blocking film 71 being partly cut out to form a light transmitting pattern 72 representing a character. LEDs 8 are arranged below the key tops 7. Each of the key tops 7 has a semitransparent screen 9 formed on a rear surface thereof in an area to be illuminated with LEDs 8 and extending only over a region opposed to the light transmitting pattern 72.