In this study, a rapid compression and expansion machine(RCEM) with a pancake combustion chamber was designed to investigate fundamentally on the knocking phenomena in spark ignition(S.I) engines. This RCEM is intended to simulate combustion in an actual engine. The homogeneous pre-mixture of n-pentane and air was charged into a quiescent atmosphere of the chamber. Then, the combustion field become simpler in this machine than it in a real S.I. engine. Also, the combustion phenomena, that is a cylinder pressure history, the behavior of flame propagation and so on, with high reproducibility are realized in this machine. The phenomena caught in this experiment were so-called low speed knocking. And, this knocking characteristics such as a knock intensity and a knock mass fraction were revealed by the cylinder pressure analysis varying the charge pressure and the equivalence ratio of the mixture, a compression ratio and an ignition timing. Then, the effects of the pressure, the temperature and the concentration of the charged mixture on the knocking characteristics were discussed. Further, the flame propagation process in the visualized combustion chamber was taken by the high-speed schlieren photography (14000f.p.s.) and also OH radical in the chamber was measured with the luminous method(6000f.p.s.). Then, an autoignition process of the endgas was revealed from the luminous images of OH radical over the chamber for several knocking phenomena.