To realize mass production as well as to improve reliability by using a backing integral construction member so as to prevent burn through, and also by forming with a semi-shear process.

The backing integral construction member is a construction member of a welded structure provided with a backing piece in a corresponding portion for the burn through while welding. The backing piece is formed by shearing the blank of the construction member into a half-blanking state and the backing piece is set within a clearance less than the wall thickness of the construction member.