To concentrate mass, to lower the center of gravity, to efficiently and optimally arrange an intake part for making a compact vehicle body. A cylinder inclined to the rear is arranged under a fuel tank and a body of an intake box is housed between a radiator arranged in front of the cylinder and the cylinder. An upper part of the body of the intake box is fixed to a body frame at the bottom of the fuel tank and air taken in is supplied to an intake port through an intake funnel and a throttle body respectively built-in. A lid of an intake duct can be extractably inserted into a window hole provided to the front of the body, a duct part integrated with the lid is arranged over the radiator, and an air intake guide port takes a flow of air in front of the radiator.