A keyboard device is provided. The keyboard device includes a baseplate, a set of keytops, a frame, and a set of plate members. The set of keytops is supported in a vertically movable manner on an upper surface side of the baseplate. The frame mounted on the upper surface side of the baseplate, and the frame includes a set of openings in which the keytops are inserted in a vertically movable manner. The set of plate members arranged along a longer direction within the baseplate, and bridges that connect adjacent plate members. The adjacent plate members are arranged with a gap provided between end surfaces thereof that oppose each other and are relatively movable through at least the bridges in a direction in which the plate members are arranged.