To unite a sub member to a main member in an inexpensive structure without lowing yield strength of the main member.

An outer reinforcement 27 which covers a prescribed range of a main member 21 including a branch part of the main member 21 and a sub member 22 from the lower side, is integrally formed with a sub lower 221 in a cross-sectional U-shape constituting the sub member 22. The outer reinforcement 27 integrally formed with the sub lower 221 is applied to cover the lower side of the main member 21 and the outer reinforcement 27 is welded and connected to the main member 21, therefore the sub member 22 consisting of the sub lower 221 which is branched and extended from a front end vicinity to an oblique front outside, is connected at the same time.