A key structure which is adjustable in pressing force required and in duration of key pushback includes a circuit board, a keycap, a first magnetic member, an elastic member, a membrane switch, and a second magnetic member. The keycap includes an extending portion. The membrane switch is spaced apart from the first magnetic member, and the elastic member buffers the first magnetic member against the membrane switch. The second magnetic member is disposed between the membrane switch and the circuit board. When energized, the second magnetic member generates magnetic attraction or magnetic repulsion to the first magnetic member. A pressing force required on the key structure and a rebound force and a delay of rebound can be dynamically adjusted by a direction and magnitude of a current applied to the second magnetic member. A key device including the key structure is also disclosed.