PURPOSE: To suppress deterioration of a fuel consumption and increase of rotational fluctuation, while preventing oil rising in a rested cylinder at the time of operating cylinder reduced operation in a multiple cylinder internal combustion engine.

CONSTITUTION: In a multiple cylinder internal combustion engine provided with an operating cylinder reducing mechanism which is available for operating cylinder- reduced-operation by resting a part of cylinder, an intake valve in a rested cylinder is maintained in its closing condition at all times when operating cylinder-reduced- operation is carried out, and also the exhaust valve of the rested cylinder is opened at the point (A) behind the bottom dead point of a piston and closed at a point (b) after a short time so as to set maximum inter-cylinder pressure of the rested cylinder to a value within the range of 5 to 12kgf/cm2 which is found out as an optimal range. Since the pressure in an exhaust manifold is nearly the atmosphere pressure, when the exhaust valve is closed in the point (b) in moving direction of a piston which is substantially in its exhaust stroke condition, the maximum internal cylinder pressure can be controlled freely because inter-cylinder pressure is raised as a positive pressure.