In case a pressure regenerator is attached to the exhaust port of a displacement type engine to regenerate the energy of an exhaust so as to realize the Atkinson's cycle, an abnormal combustion or a fusion of an exhaust valve occurs in a 4-cycle engine if a regenerative pressure is raised. This problem is solved by using a 6-cycle engine as the displacement type engine. The 6-cycle engine with the regenerator can change the output ratio between the 6-cycle engine and the regenerator so that it can be utilized as either an engine for generating two kinds of outputs by using that principle or a highly controllable 6-cycle gas turbine. This internal combustion engine is excellent and useful in the mileage as a prime mover from a power plant to a small generator or as an engine to be mounted on a mover such as a ship or a car. The internal combustion engine is especially suitable for the mover such as a hybrid car. Incidentally, the 6-cycle engine is ready for license agreements.