PURPOSE: To start a two-cycle operation during acceleration of a two-four switching engine by increasing a supercharge pressure, and switching intake/ exhaust mechanisms of the engine and an injection timing.

CONSTITUTION: Switching clutches 23, 43 are provided respectively on a two-cycle exhaust valve 2, a four-cycle exhaust valve 4 and an intake valve 45 arranged on a cylinder head 12. An intake shutter 33 and a closable intake port 14 are formed on an intake passage for two cycle. A supercharge pressure of a turbocharger 3 is increased during acceleration based on signals of an engine speed sensor 16 and an engine load sensor 62 by electrically driving a rotary motor 35. Mechanisms of the above-mentioned intake/exhaust passages and an injection pump 6 is controlled for two cycle. An engine is thus operated so as to obtain a high output.