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 of the catalyst case is equal to an inside diameter 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 of the catalyst case is equal to an inside diameter 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.