To solve such problems of a rotary engine comprising, in a housing 1 having an enlarged part and a reduced part, vanes 3 provided in a plurality of radially located lateral grooves from a center of a rotor 2 for successively carrying out four steps of sucking, compressing, exploding and exhausting an air-fuel mixture while keeping airtightness by a spring 8 or centrifugal force, that though the rotary engine is to work theoretically, frictional force actually increases due to the centrifugal force working as the rotation increases, and the engine rotates to some degree but does not contribute to practical use due to the damage of an internal surface of the housing 1 and the vane 3.

To control the centrifugal force working to the vane 3, which is a big disadvantage, the centrifugal force is balanced by a balance lever 4A or a balance disk 4 and an arcuate vane 3, thereby preventing damage of the housing 1 and damage of an apex seal 7. Thus, a feasible rotary engine capable of keeping smooth rotation and reliable airtightness is obtained.