Lightning-protection fastener, the lightning protection fastener cap

The present invention provides a lightning-proof fastener able to reliably seal an arc between a cap and a wing panel. One end (30a) of the cap (30A) on the open side opposing member (22), or member (21), has a flat surface (30d) orthogonal to the axis of the cap (30A), and a tapered surface (30c) formed on the outer peripheral side of the flat surface (30d). Sealant (34), or sealant (34S), overflowing from the cap (30A) once the cap (30A) has been installed is interposed between the tapered surface (30c) and the surface (22f) of the member (22).