An exhaust device for a motorcycle comprising: a plurality of primary exhaust pipes (33A, 33B, 33C, 33D), each of which is connected to a cylinder of a multi-cylinder engine body mounted on a body frame, a collecting exhaust pipe, which is connected in common to the downstream end portions of the primary exhaust pipes (33A - 33D), wherein said collecting exhaust pipe has a contour body, which consists of a pair of contour members (48, 49) connected to each other so as to form therebetween an exhaust gas flow passage for the exhaust gas guided from the said plurality of primary exhaust pipes (33A - 33D), and partition wall members (45, 46), which are connected to said contour body while being sandwiched between said contour members (48, 49) so as to divide the inside of said exhaust gas flow passage into at least two, wherein a plurality of swelling portions (53,54), which project towards said other contour member, are formed on at least one of said contour members (48, 49), in order to form tubular undulations (51, 52), which have a tubular shape similar in appearance to said plurality of primary exhaust pipes (33A - 33D) and extend continuously and respectively in the same direction as the primary exhaust pipes (33A - 33D) on at least one outer surface of said contour body, and said partition wall members (45, 46) are connected to said contour body at a location spaced from the portions (53a, 54a) of said swelling portions (53, 54) which are swollen toward the inside of the collecting exhaust pipe out of the tubular undulations (51, 52) and extend from an upstream region to a downstream region of said contour body in the direction of exhaust gas flow in said exhaust gas flow passage; characterized in that the upstream and downstream end portions in the direction of exhaust gas flow of said partition wall members (48, 49) are connected and form a hollow portion between the intermediate portions of the partition wall members (48, 49), and said partition wall members (48, 49), which divide said exhaust gas flow passage into two branch flow passages (56, 57), are connected to said contour body so as to be sandwiched between said contour members (48, 49). a plurality of primary exhaust pipes (33A, 33B, 33C, 33D), each of which is connected to a cylinder of a multi-cylinder engine body mounted on a body frame, a collecting exhaust pipe, which is connected in common to the downstream end portions of the primary exhaust pipes (33A - 33D), wherein said collecting exhaust pipe has a contour body, which consists of a pair of contour members (48, 49) connected to each other so as to form therebetween an exhaust gas flow passage for the exhaust gas guided from the said plurality of primary exhaust pipes (33A - 33D), and partition wall members (45, 46), which are connected to said contour body while being sandwiched between said contour members (48, 49) so as to divide the inside of said exhaust gas flow passage into at least two, wherein a plurality of swelling portions (53,54), which project towards said other contour member, are formed on at least one of said contour members (48, 49), in order to form tubular undulations (51, 52), which have a tubular shape similar in appearance to said plurality of primary exhaust pipes (33A - 33D) and extend continuously and respectively in the same direction as the primary exhaust pipes (33A - 33D) on at least one outer surface of said contour body, and said partition wall members (45, 46) are connected to said contour body at a location spaced from the portions (53a, 54a) of said swelling portions (53, 54) which are swollen toward the inside of the collecting exhaust pipe out of the tubular undulations (51, 52) and extend from an upstream region to a downstream region of said contour body in the direction of exhaust gas flow in said exhaust gas flow passage; characterized in that the upstream and downstream end portions in the direction of exhaust gas flow of said partition wall members (48, 49) are connected and form a hollow portion between the intermediate portions of the partition wall members (48, 49), and said partition wall members (48, 49), which divide said exhaust gas flow passage into two branch flow passages (56, 57), are connected to said contour body so as to be sandwiched between said contour members (48, 49).