A top board structure capable of easily and simply assembling and welding a reinforcing frame to a top board body, providing a sufficient strength with a reduced weight, and reducing abnormal noise that might occur when an impact is applied. A reinforcing frame formed by assembling lateral reinforcing member directed in a lateral direction with a longitudinal reinforcing member directed in a longitudinal direction is fixed to the lower surface of a base board in a top board body formed at the peripheral edge thereof in a box shape opened downward by a downward piece, a rear surface cover in a box shape opened upward by an upward piece is formed at the peripheral edge of a cover base board, and the rear surface cover is fixed to the top board body with the upward piece of the rear surface cover kept fitted/inserted into gaps formed between the inside surface of the erect piece portion of the downward piece in the top board body and the outside portion of the reinforcing frame or the inside partition wall of the reinforcing member constituting the reinforcing frame.