In order to raise thermal efficiency and to reduce exhaust emissions of pre-chamber type gas engines, it is important to understand combustion phenomena inside of pre-chamber and flame-jet behaviors into main chamber. A constant volume vessel[0] was used to simulate combustion in pre-chamber type gas engines. We observed combustion phenomena in the pre-chamber and flame-jet behaviors in the main chamber using high-speed direct photography and Schlieren photography We found that the change of the igniter position in the pre-chamber showed significant changes in combustion regime in the main chamber. We also found that a change in the shape of the connecting nozzle has promoted mixing and combustion in the main chamber.