The invention provides a keyboard device for an electronic musical instrument with light weight and low price. The keyboard frame comprises a front plate, a rear plate, a vertical plate, an extending set and a plurality of reinforced ribs. The width of the front and the rear plate at the length direction of the key is wide, and the front and the rear plate are extendingly disposed at the arranging direction of the key. The rear end of the front plate and the front end of the rear plate are extendingly disposed at the arranging direction of the key and are connected to a vertical plate. The width of the extending set at the length direction of the key is narrow , and is extendingly disposed at the arranging direction of the key at the position of leaving the front plate and heading to the front. The reinforced rib is a thin plate extendingly disposed at the arranging direction of the key with a regulated interval. The front plate, the rear plate and the extending set and the plurality of reinforced ribs are integrated into one piece by connection. A boss for assembling components is disposed at the connecting part of the reinforced rib and the extending set.