PURPOSE: To enlarge a radiator mounting space so that a radiator is located at a high position by extending a downtube from a point apart from a head pipe downwardly at an accute angle.

CONSTITUTION: The radiator b is arranged in the space surrounded by a front fork 6, a front fender 7 and the downtube 11. The donwtube 11 is extended from the point apart from the head pipe downwardly at the accute angle and fixed to a main pipe 10. As a consequence, the radiator mounting space is much enlarged, thereby eliminating a possible of interference occurring by other members. Further, the radiator can be located at a relatively high position, and therefore, the radiator can be protected from attachment of mud and the like.