PURPOSE: To prevent natural ignition even in case of increasing the compression ratio by using a valve united in one body with an auxiliary combustion chamber capable of air intake and air intake stoppage through turning a modified type of valve so as to provide two independent necessary functions of a valve for the auxiliary combustion chamber.

CONSTITUTION: Transmission of the pressure of a main combustion chamber to an auxiliary combustion chamber can be reduced or intercepted by turning or reversely turning a modified type of valve 1, and the number of valve function required for air intake is two. Further, by changing shapes of slit parts A, B, the valve 1 works as a completely independent valve united in one body with the auxiliary combustion chamber which intercepts the pressure of the main combustion chamber during compression so that the pressure is not applied from the main combustion chamber to the auxiliary combustion chamber, and also works as the valve united in one body with the auxiliary combustion chamber which is a conventional auxiliary combustion type of the main chamber and the auxiliary chamber in connection with each other.