An electricity generation system includes an internal combustion engine and at least one electricity generation motor that generates electricity upon an input shaft thereof being rotated by the internal combustion engine, wherein the internal combustion engine includes: a piston reciprocable in a cylinder; a valve actuating mechanism that actuates an intake valve and exhaust valve; a supercharger that compresses intake air to be delivered into the cylinder; and a fuel feeder, and wherein while the piston reciprocates once by starting from a top dead center and returning to the top dead center, the valve actuating mechanism actuates the intake and exhaust valves in such a manner as to provide a valve overlap period, the fuel feeder feeds fuel into the cylinder after closing of the exhaust valve, and an air-fuel mixture inside the cylinder is burned during a period in which both of the intake and exhaust valves are closed.