A keyboard comprises a key module and a backlight module in which the key module comprises a light-transmissive key part and an electric circuit substrate, and the backlight module comprises a light guide plate, a reflection unit and at least one light source. The backlight module is disposed between the key part and the electric circuit substrate. Thus, lights emitted by the light source are projected into the light guide plate from the lateral side of the light guide plate, and the lights are reflected by the reflection unit for directly passing through the light output surface of the light guide plate and the key part.