A head pipe includes a pipe portion and a bracket portion contiguously formed on a rear portion of the pipe portion wherein front end portions of the main frames and a front end portion of the down frame are jointed to the bracket portion. A widthwise center line of the main frames in the vertical direction is directed toward an intermediate portion of the pipe portion in the vertical direction in a side view. An upper surface extension line and a lower surface extension line on the extension in the frontward direction of an upper surface and a lower surface of the main frames pass between an upper end and a lower end of the pipe portion as viewed in a side view. The down frame is inclined to be directed towards the intermediate portion of the pipe portion in the vertical direction as viewed in a side view.