A keyboard apparatus for an electronic musical instrument has a metallic keyboard chassis and a balance rail provided on the keyboard chassis. A plurality of pins are provided on the balance rail. The pins and the balance +*rail constitute fulcrums for swingably supporting white keys and black keys. The fulcrums for the black keys are disposed on the same line with, or in front of, the fulcrums for the white keys. Hammers are provided in a rear of the keys so as to be swingable by swinging of each of the respective keys. The hammers are disposed on the same axis of rotation, and a position for the black keys to operate to swing the respective hammers is located in front of a position for the white keys to operate to swing the respective hammers such that an angle of rotation of the respective hammers becomes substantially equal to each other. A stopper member for restricting the swinging movement of the keys or the hammers are provided in a rear upper portion of the keys. The metallic key board chassis is divided into a front chassis portion and a rear chassis portion, and the two are connected by metallic reinforcing beams.