PURPOSE: To provide such a cycle changeable engine as capable of changing itself to two cycle drive and/or four cycle one according to the speed and load of one engine.

CONSTITUTION: An intake valve 11, which is closed at the time of two cycle drive but opened at proper timing in time of four cycle drive, is set up on top of a cylinder 1, and an intake port 15 is installed in a lower part of this cylinder 1. A sleeve valve, having an intake window opening this intake port and consisting of a magnetic body, is fitted in the cylinder in a part of the intake port 15, energizing an electric current to plural pieces of copper pins forming a driven part installed in the sleeve valve and shifting them in the circumferential direction by dint of electromagnetic force with a magnetic field of an electromagnet from the outside, and the intake port is controlled so as to make it open at two cycle drive and close at four cycle drive, respectively.