PURPOSE: To produce optimum concentrated mixture gas, to improve combustion efficiency, to expect the decrease of combustion carbon, to relieve the explosion force of an operation chamber in a closed state through operation of a shield member, and to buffer an impact on a main rotor.

CONSTITUTION: Main and. auxiliary chambers 2 and 3 are formed at a rotary casing 1 through a communication passage 6 and an eccentrically rotating auxiliary rotor 13 in a round shape is arranged to an auxiliary chamber 3 in a round shape. A shield member 16 making constant contact with the auxiliary rotor is retractably arranged on the wall surface of the auxiliary chamber. The auxiliary chamber is formed such that a mixture gas producing chamber is formed in the auxiliary chamber by using the auxiliary rotor and the shield member 16, a main rotor 7 in a round shape is arranged in the main chamber 2 in an eccentric shape, and an actuating chamber 8 is formed in the main rotor. Further, a two-rotor system rotary engine comprises the main chamber having a shield member 9 which partitions the actuating chamber away from the gap part 2a of the main rotor and is rockably and retractably arranged to the main rotor.