A keyboard device is provided with a base plate configured by arranging a plurality of plate members, a plurality of keytops vertically movably supported on the upper surface side of the base plate, a frame attached to the upper surface side of the base plate and having a plurality of hole portions into which the keytops are vertically movably inserted, and a fastening tool provided at a position overlapping with a plate boundary portion formed between the facing end surfaces of the plate members adjacent to each other and simultaneously fastening the adjacent plate members to the frame.