A main pipe of a motorcycle is enhanced in stiffness to stably support an engine. The main pipe includes an intermediate pipe extending above the engine in a longitudinal and substantially horizontal direction, a front pipe extending forwardly downwardly of the engine from a front end of the intermediate pipe, and a rear pipe extending rearwardly downwardly of the engine from a rear end of the intermediate pipe. The rear pipe is curved arcuately in a manner to go around a pivot shaft forwardly downward from a rear side thereof and the engine is connected to a lower end side of the rear pipe.