To provide a complete slit material effectively preventing the collapse of a column in the case of an earthquake.

A hollow section 1 in the longitudinal direction is formed in the slit material made of polyvinyl chloride, flat exterior walls 2a, 2b opposed, holding the hollow section 1 are bulged continuously to the outside in the longitudinal direction respectively, ceramic fibers are used as a fire resistive material for both side edge sections and the insides of connecting members 7a, 7b, long-shaped flat form curved sections are formed integrally in the shapes that the curved sections are lowered to the insides of the ceramic fibers sections. A reinforcing material 3 having cushioning properties to external force from the flat exterior-wall sides 2a, 2b in the hollow section 1 are formed integrally along the longitudinal direction, voids 8a, 8b for installing the fire resistive material are formed in the longitudinal direction on the bottom sections of fitting grooves 4a, 4b, and the connecting members 7a, 7b connecting the internal surfaces of the fitting-grooves side walls 5a, 5b, 5c, 5d are mounted movably at the base end edges sections of the side walls 5a, 5b, 5c, 5d of the fitting grooves in order to control the quantity of the front-end edge sides opened of the fitting grooves 4a, 4b to a fixed quantity or less.