TWO-STROKE ENGINE

This two-stroke engine (101, 102) is capable of performing at least a gas mode operation using a flammable gas as a main fuel, and includes a plurality of cylinders (1), an exhaust valve (13) provided in each of the plurality of cylinders (1), and an air-fuel ratio controller (70, 74). At a time of the gas mode operation, the air-fuel ratio controller (70, 74) has: a function of calculating an average air-fuel ratio inside the plurality of cylinders (1), and of controlling the average air-fuel ratio by adjusting an air flow volume which is supplied to the plurality of cylinders (1); and a function of calculating an air-fuel ratio inside each cylinder (1), and of controlling the air-fuel ratio by adjusting a closing timing of the exhaust valve (13).