A key structure includes a movable element, an elastic element, a light-emitting element and a pressure sensing element. The pressure sensing element is arranged between the elastic element and the light-emitting element. The elastic element is disposed on the movable element. The light-emitting element emits a light beam. The light beam is transmitted through the pressure sensing element and projected to the movable element to illuminate the key structure. While the key structure is depressed, the elastic element is pushed by the movable element. The pressure sensing element is pushed by the elastic element according to different magnitudes of the depressing force. Consequently, the key structure generates different pressure sensing signals.