A keyboard device includes plural key structures, a switch circuit board, an elastic cover and a seal element. The switch circuit board includes a hollow region. The elastic cover is disposed on the switch circuit board. The hollow region is covered by the elastic cover, so that a foreign liquid is prevented from entering the switch circuit board. The seal element is disposed on sidewalls of the switch circuit board. Consequently, a sealed region is formed between the switch circuit board and the elastic cover. When the inner gas within the switch circuit board is changed, the elastic cover is subjected to expansion or contraction. Consequently, the switch circuit board is not subjected to deformation in response to the volume change of the inner gas.