To make a sash function rationally as a thunder receiver of a rotation sphere method, and to constitute the thunder receiving portion of the rotation sphere method rationally in a sidewall having a metallic portion other than a sash.

In this sidewall protection mechanism from thunder in a building, a projection 5 of the thunder attacking portion is protrusively formed from the metallic structure 3 of the sash on the surface side of the outer wall 1 constituted of the sash 2. This metallic structure and a conductive member constituting the body of the building are electrically connected by an electric conductor.