PURPOSE: To fix a protecting slab under an excellent state for a prolonged term by arranging the protecting slab between a mounting member mounted on the side face of a roof rising section and a rail-shaped member in a lower section and sliding a rocking preventive body.

CONSTITUTION: A protecting-slab holding section 4 consisting of a front plate 2a and a rear plate 2b drooped from a drooping piece 5 at a regular interval is formed to an approximately F-shaped sectional mounting member body 2. Projecting strips 2c along the longitudinal direction are formed to the internal side face of the front plate 2a or the rear plate 2b. A rocking preventive body 3 with a horizontal piece 3b and recessed grooves 3a is installed slidably to the mounting section body 2 while the recessed grooves 3a are fitted slidably to the projecting strips 2c. The mounting member 2 is set up onto the side face of a roof rising section, and a rail-shaped member is laid to the vertical lower section of the holding section 4. A protecting slab is fitted between the holding section 4 and the rail-shaped member in a vertically moved cover manner, and the rocking preventive body 3 is slid, thus fixing the upper end of the protecting slab.