To provide a rotary modulation engine, which has reduced number of parts, volume and cost, and provides effectively improved operation efficiency.

The rotary modulation engine is equipped with a first transmission mechanism 500, a second transmission mechanism 600, a spark plug 14, an intake manifold 18, and an exhaust manifold 19. The first transmission mechanism 500 has a housing, two sets of rotors, and two elliptical gears 1, 4. The housing has a cylindrical outer cylinder wall 11 and a cylinder cover 21. An intake hole and an exhaust hole are arranged on the outer cylinder wall 11. Through holes are provided on both sides of the hosing. The two sets of rotors are arranged in the housing, and have shaft centers 15, 16, a circular inner cylinder wall, and two rotary pistons. The shaft centers 15, 16 of the rotor are extended through the center of the inner cylinder wall.