To weld a flat plate member to a flat base material by a method in conformance with an arc stud welding.

A welding convex part 11 having an approximately vertical side face 12 on a periphery is processed to a flat plate member 1, and a front face of the convex part 11 contacts with a flat base material 2 and the current is conducted. A gap g is formed on the contact face while the current is applied so as to generate an arc. Then, the convex part 11 is melted, and is closely touched to the flat base material 2.