Problem It is an object of the present invention to provide a catalyst arrangement construction of a motorcycle 10 where a compact arrangement is available while a lowest ground height is ensured. Solution An engine 211 has a crankcase 214, and a cylinder 215 which extends from an upper portion of the crankcase 214 toward a front side. In a space which is formed at an upper side of a horizontal surface which substantially horizontally extends from a bottom surface of the crankcase 214, a catalyst storage chamber 280 is arranged in such a manner that an axis L of the catalyst converter 280 is in a direction of a crankshaft CR. The space is arranged just below a front surface of the cylinder 215 and forward of a front surface of the crankcase 214.