A straddled vehicle comprising: an internal combustion engine including a crankcase supporting a crankshaft such that the crankshaft is rotatable, a cylinder body extending upward from the crankcase , a cylinder head extending upward from the cylinder body , the cylinder head including a front wall , and an exhaust port defined in the front wall of the cylinder head , the exhaust port being configured to discharge exhaust gas; an exhaust pipe including an upstream end and a downstream end , the upstream end being connected to the exhaust port , the exhaust pipe being configured to allow the exhaust gas to flow therethrough; an expansion chamber case including an inlet and an outlet , the inlet being connected to the downstream end of the exhaust pipe , the expansion chamber case being internally provided with an expansion chamber to expand the exhaust gas; a catalyst case including an inlet connected to the outlet of the expansion chamber case ; and a catalyst disposed inside the catalyst case , wherein at least a portion of the catalyst case overlaps with the cylinder body in a vehicle side view, a volume of the expansion chamber is larger than an inner volume of the catalyst case , and the expansion chamber case is curved with a first portion extends upward from the inlet and with a second portion that extends rearward from the first portion to the outlet in the vehicle side view, characterized in that the catalyst case has a cylindrical shape, and an outside diameter (D40) of the catalyst case is equal to an inside diameter (D32) of the outlet of the expansion chamber case and a vehicle width outer end of the expansion chamber case is located inward of a vehicle width outer end of the crankcase in a vehicle width direction. an internal combustion engine including a crankcase supporting a crankshaft such that the crankshaft is rotatable, a cylinder body extending upward from the crankcase , a cylinder head extending upward from the cylinder body , the cylinder head including a front wall , and an exhaust port defined in the front wall of the cylinder head , the exhaust port being configured to discharge exhaust gas; an exhaust pipe including an upstream end and a downstream end , the upstream end being connected to the exhaust port , the exhaust pipe being configured to allow the exhaust gas to flow therethrough; an expansion chamber case including an inlet and an outlet , the inlet being connected to the downstream end of the exhaust pipe , the expansion chamber case being internally provided with an expansion chamber to expand the exhaust gas; a catalyst case including an inlet connected to the outlet of the expansion chamber case ; and a catalyst disposed inside the catalyst case , wherein at least a portion of the catalyst case overlaps with the cylinder body in a vehicle side view, a volume of the expansion chamber is larger than an inner volume of the catalyst case , and the expansion chamber case is curved with a first portion extends upward from the inlet and with a second portion that extends rearward from the first portion to the outlet in the vehicle side view, characterized in that the catalyst case has a cylindrical shape, and an outside diameter (D40) of the catalyst case is equal to an inside diameter (D32) of the outlet of the expansion chamber case and a vehicle width outer end of the expansion chamber case is located inward of a vehicle width outer end of the crankcase in a vehicle width direction. <EOS>