To enable execution of construction and disassembly-removal in a short period, to simplify a process of construction and to enable reuse of a wall material.

This structure of an inner wall surface is equipped with an interior board for building provided with a linear reinforcing member 2, a linear support member 10 fixed to a wall body W and an engagement fitting 20 fixed to the support member and to be engaged with the reinforcing member. The reinforcing member has a part 9 opening toward the support member and this opening part is formed of an engagement part 8 which can open and close elastically. An enlarged head part 21 of the engagement fitting expands the engagement part, opens the opening part in an expanding manner and passes through this part when it is pressed to the engagement part of the reinforcing member. The peripheral edge on the base end side of the enlarged heat part engages with the engagement part when the heat part passes through the opening part. The peripheral edge on the base end side is formed to be smooth, and when an external force exceeding a prescribed load acts in the direction of pulling the linear reinforcing member and the engagement fitting apart from each other, it expands the engagement part, opens the opening part in an expanding manner and is pulled out from this part.