To cover or support the end section of a siding board in various modes by fixing a metal thin plate having a patter on the outer surface on the outside of an accessory main body made of an extrusion-molded material.

Many siding boards 1 are arranged from above to below in sequence while their both ends are matched, and large-area wall sections A, B adjacent on the right and left are formed. A grained shallow irregular pattern is applied on the outer surface of an accessory 10. The accessory 10 is used in combination with a support fixed on the backing side of a pillar 5 located between the siding boards 1 of the wall sections A, B. A fitting projection 13 protruded at the center of the back face of the main body 11 of the accessory 10 is inserted between a pair of support pieces 8 of the support 6, engaging pawls 13a formed on both sides of the fitting projection 13 are engaged with the engaging sections on the inner faces of the support pieces 8, and the accessory 10 is connected to the support 6 while the end sections of the siding boards 1 are pinched.