Abstract: A rotary engine is disclosed which comprises a rotor housing, a rotor fitted in the rotor housing so as to define a plurality of operating chambers in cooperation with the inner wall surface of the rotor housing and produce a planetary rotation of itself inside the rotor housing, apex seal members severally accommodated inside seal grooves formed at the apexes of the rotor along the axis of rotation of said rotor, and pressure means disposed between the respective apex seal members and the rotor so as to press the apex seal members against the inner wall surface of the rotor housing by virtue of the pressure of a gas emanating from the operating chambers.