To smoothly switch operation cycle in a variable cycle engine.

In the engine switching two-cycle, four-cycle, six-cycle operation according to engine speed and a required load, switching of the cycle is executed at the following timing, for each cylinder. Switching between the two-cycle and the four-cycle is executed at timing when explosion strokes of both cycle coincides with each other (arrows A, B). Switching between the four-cycle and the six-cycle is executed in a section D1(arrows C, D) where intake/compression stroke of both cycle coincides with each other, or a section D2(arrows E, F) where the intake/compression strokes, the explosion strokes, and an exhaust strokes of both cycle coincides with each other. Therefore, abnormal combustion and torque shock are suppressed, thereby smoothly carrying out switching.

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