Key structure for keyboard

A key structure for a keyboard, the keyboard comprising a top plate, and the top plate being comprising a socket, wherein the key structure comprises:

• a lower housing having comprising a base, wherein an annular stopper is protruded above an outer side of the base, two engaging elastic arms disposed below opposite sides of the annular stopper are protruded below the outer side of the base toward a direction of approaching the annular stopper, the lower housing engages with the socket by compressing the two engaging elastic arms, and the top plate is disposed between the annular stopper and the two engaging elastic arms;
• an upper housing disposed above the lower housing, the upper housing comprising a penetrating opening;
• a pressing shaft movably disposed between the lower housing and the upper housing, a top end of the pressing shaft penetrating through the penetrating opening;
• and
• a spring elastically supported between the lower housing and the pressing shaft.