A key structure includes a keycap, a supporting plate, a connecting element, a circuit board and an elastic element. The circuit board is disposed on the supporting plate. The circuit board includes a switch element. A first switch unit of the switch element is formed on a top surface of a first film layer of the circuit board. A second switch unit of the switch element is formed on a top surface of a second film layer of the switch element. When the keycap is depressed in response to an external force, the elastic element is subjected to deformation. Consequently, the first switch unit and the second switch unit are selectively turned on to generate a first key signal and a second key signal.