PURPOSE: To control the opening/closing conditions of respective valves in response to the operation condition of an engine, by providing detecting means which detect the operation condition of the engine, and a controller which controls the operation conditions of respective valves in response to detection signals from these detecting means.

CONSTITUTION: The operation conditions of an engine rotation number and a load or the like are detected by means of detecting means 14, 31. A controller 15 controls the opening/closing condition of respective valves 1, 2, 12 in response to the operation condition of the engine by inputting these detection signals into the controller 15. Accordingly, the engine can be changed over to 2 cycles or 4 cycles, and at the same time can be changed over to a direct injection type combustion condition or a sub-chamber type combustion condition, and especially, control which can restrain the generation of NOx against the whole operation sphere of the engine, can be conducted.