COMBUSTION PRESSURE CONTROLLER

A combustion pressure control system of a spark ignition type of internal combustion engine which has a sub chamber 60 which is communicated with a combustion chamber 5, wherein the system is provided with a volume changing device which changes a volume of the sub chamber 60 by a change of pressure of the combustion chamber 5 serving as a driving source when the pressure of the combustion chamber 5 reaches a control pressure. The control pressure is set in a range of larger than a maximum pressure of the combustion chamber 5 in the case of suspending the supply of fuel and less than the pressure at which abnormal combustion of the fuel occurs. The volume changing device is formed so that when the pressure of the combustion chamber 5 reaches the control pressure during the period from a compression stroke to an expansion stroke of a combustion cycle, the volume of the sub chamber 60 becomes larger and a rise of the pressure of the combustion chamber 5 is suppressed.