PURPOSE: To prevent the generation of reverse propelling force by providing ignition chambers in the explosion positions of an outer cylinder, and setting the ignition chambers so that pressure at the time of explosion is applied as vartically as possible to vanes.

CONSTITUTION: Directional ignition chambers 26 are installed in an opposed explosion type rotary engine, and an outer cylinder is formed being divided into an intake compression cylinder 3 and an explosion exhaust cylinder 4, so that simultaneous explosions can be generated twice during one rotation. At this time, the explosion pressure direction of the ignition chambers 26 is set into the direction of applying pressure in a relatively vertical directions to the side faces of vanes 7, 8 in the rotating direction of a rotor 2 or the pressure receiving faces corresponding to the vanes 7, 8. The pressure directions 13 at the time of explosion therefore act parallel to the surface of the rotor 2, so that the effective propelling force of the vanes 7, 8 is increased, and the output efficiency of the rotary engine can be improved.