A cover member of a vehicle body outer panel coupling part covers a step portion with a height difference that is just the thickness of a sheet thickness, by overlapping a roof side rail outer panel, which has a surface that continues to a surface of a vehicle body, on a center pillar outer panel, which has the surface. The cover member comprises: a cover body that is attached to a coupling recess, and is obtained by mixing a magnetic power with a thermoplastic resin; and an adhesive resin layer that is applied to an attachment surface that forms an inner surface facing the center pillar outer panel and the roof side rail outer panel of the cover body.