To effectively reinforce a secion in a vicinity of a pivot in a motorcycle body frame.

A down tube 18 extends downwardly from a head pipe 3, and an upper frame 21 extends backwardly. A seat frame 23 extends backwardly from a rear end of the upper frame 21, and a pair of rear arm brackets 24 extend downwardly. A seat pillar 40 is connected between a middle position of the rear arm bracket 24 and a rear end of the seat frame 23. A lower end of the rear arm bracket 24 is joined with a pivot fitting cylinder 26 passing through the pivot 28. A front end of a rear arm 27 is supported by a pivot 28 on the outer side of the pivot fitting cylinder 26. A main reinforcing frame 45 is stretched between the middle position of the seat pillar 40 and the pivot fitting cylinder 26.