To detach or attach a part of a frame in a semi-double cradle type vehicle body frame, simplify a structure, reduce a number of parts, reduce costs, and reduce a weight.

This structure comprises a head pipe 102, a single down tube 113 extending backward and downward from the head pipe 102, and a pair of right and left lower tubes 114R, 114L branched at a lower bottom of the down tube 113. One lower tube 114L is detachable. The lower tube 114L comprises a tube member 114a, a front side connection part 114b communicated with a front end of the tube member 114a, and a rear side connection part 114c communicated with a rear end of the tube member 114a, and a side stand mounting part 5 is integrally formed on the rear connection part 114c. Also, a front end (front connection part 114b) of the lower tube 114L is bolted to the connection part 134 of the down tube 113 together with an engine suspension plate 135.