An object of the present invention is to allow a flap of a roll storage case to be easily opened and closed by means of a flap cover and to prevent the flap cover from slipping off from the flap of the roll storage case even when the flap is opened and closed many times. A flap cover includes an upper plate covering an upper surface portion of a flap, a front plate covering a front surface portion of the flap, and a pair of side plates covering opposite side surface portions of the flap. Each of the side plates includes a locking portion which projects inward from the side plate and which is able to be locked on a lower end surface of the side surface portion of the flap.