Keyboard device and key structure thereof

A keyboard device comprising plural key structures, each of the plural key structures comprising:

• a base plate;
• a keycap located over the base plate, wherein the keycap comprises a pressing post, and the pressing post is protruded in a direction toward the base plate;
• a membrane circuit board arranged between the base plate and the keycap;
• a connecting member penetrated through the membrane circuit board and connected between the keycap and the base plate, wherein the keycap is movable upwardly or downwardly relative to the membrane circuit board through movement of the connecting member;
• and
• an elastic element arranged between the keycap and the membrane circuit board, and comprising a resilience piece and plural supporting ribs, wherein the resilience piece of the elastic element has a semi-spheric shell structure, and the semi-spheric shell structure has a cavity facing the membrane circuit board and the plural supporting ribs are arranged between the resilience piece and the keycap, and the plural supporting ribs are formed on the semi-spheric shell structure of the resilience piece and protruded in a direction toward the keycap and contacted with the pressing post of the keycap, so that there is a gap between the pressing post and the resilience piece.