An engine comprising: a cylinder block having a cylinder; a cylinder head attached to the cylinder block, the cylinder head having an exhaust port communicating with the interior of the cylinder; and a catalyst storage case attached to the cylinder head, wherein the catalyst storage case comprises: a case body having an inlet, an outlet, and an exhaust passage extending from the inlet to the outlet for allowing exhaust gas to pass therethrough; and a plurality of oxidation catalysts (61;62) disposed in the exhaust passage of the case body, wherein the plurality of oxidation catalysts are arrayed in a direction intersecting a direction along which the exhaust passage extends; wherein the inlet of the catalyst storage case is in communication with the exhaust port of the cylinder head; the cylinder block has a piston disposed in the cylinder and a crankshaft coupled to the piston, the cylinder block has a load-side end face from which a load-side end of the crankshaft protrudes, wherein the engine is characterized in that: the catalyst storage case is disposed toward the load-side end face of the cylinder block, and the longitudinal axes of the plurality of oxidation catalysts (61;62) in the catalyst storage case are in a plane orthogonal to the axis of the shaft center of the crankshaft. a cylinder block having a cylinder; a cylinder head attached to the cylinder block, the cylinder head having an exhaust port communicating with the interior of the cylinder; and a catalyst storage case attached to the cylinder head, wherein the catalyst storage case comprises: a case body having an inlet, an outlet, and an exhaust passage extending from the inlet to the outlet for allowing exhaust gas to pass therethrough; and a plurality of oxidation catalysts (61;62) disposed in the exhaust passage of the case body, wherein the plurality of oxidation catalysts are arrayed in a direction intersecting a direction along which the exhaust passage extends; wherein a case body having an inlet, an outlet, and an exhaust passage extending from the inlet to the outlet for allowing exhaust gas to pass therethrough; and a plurality of oxidation catalysts (61;62) disposed in the exhaust passage of the case body, wherein the plurality of oxidation catalysts are arrayed in a direction intersecting a direction along which the exhaust passage extends; wherein the inlet of the catalyst storage case is in communication with the exhaust port of the cylinder head; the cylinder block has a piston disposed in the cylinder and a crankshaft coupled to the piston, the cylinder block has a load-side end face from which a load-side end of the crankshaft protrudes, wherein the engine is characterized in that: the catalyst storage case is disposed toward the load-side end face of the cylinder block, and the longitudinal axes of the plurality of oxidation catalysts (61;62) in the catalyst storage case are in a plane orthogonal to the axis of the shaft center of the crankshaft. the catalyst storage case is disposed toward the load-side end face of the cylinder block, and the longitudinal axes of the plurality of oxidation catalysts (61;62) in the catalyst storage case are in a plane orthogonal to the axis of the shaft center of the crankshaft.