A key switch includes a switching member supported on a resilient member and connected to a key cap and driven by it to slide in a locating member. The switching member has two opposite, curved side plates caused to slide in the locating member along two opposite sliding ways. The elastic member has a plurality of small raised portions supported on the PC board, a plurality of spaced ribs on the inner wall surface to reinforce the structure and the elastic resilient property thereof, and a plurality of notches between the raised portions for exhaust of air squeezed by the circular flange of said switching member.