Abstract: A saddle-riding type vehicle including a simple, lightweight and high rigidity frame structure. The frame structure includes bending upward center pipes 22, which are joined to lower pipes 21 extending backward from the lower portions of a pair of right and left front pipes 20, respectively; connecting the front pipes 20 to the center portions of the center pipes 22 with straight main pipes, respectively; putting front side pipes 25 between the front pipes 20 and the lower pipes 21 for constituting the three-sides of triangles together with the front pipes 20 and the lower pipes 21, respectively; extending seat rail pipes 26 backward from the center portions of the main pipes 24 by way of cross pipes 23 put between the upper portions of the center pipes 22, respectively; and laying reinforcing pipes 27 put between the front side pipes 25 and the main pipes 24 on the same straight lines as those of the seat rail pipes, respectively.