PURPOSE: To rapidly improve exhaust gas purifying performance and to ensure excellent operability by a method wherein, when during cold running, the resistance increasing means of an exhaust passage is actuated, the opening working area of an intake air auxiliary port is varied to the high rotation side.

CONSTITUTION: A rotary engine 10 is provided with an SM port 20b and an SA port 20a as an intake air port in addition to a primary. A CPU 40 actuates an exhaust control valve 24 during cold running to increase a pressure in an exhaust manifold 22, and an exhaust gas temperature is increased through heat insulation compression to increase the activating speed of a converter 23. During operation, a working area where a control valve 26 of a secondary auxiliary intake air port 20a is opened is varied to the high rotation side by means of an actuator 25. When the number of revolutions of an engine detected by a sensor 29 exceeds the working area, the control valve 26 is opened to reduce an internal EGR. This constitution rapidly ensures exhaust gas purifying performance, and ensures good operability in a high rotation area.