PURPOSE: To rotate a rotary disk efficiently by constituting a system in such a way that the rotary disk can close directly a combustion gas exhaust nozzle of a combustor.

CONSTITUTION: Four combustors 3, 3 are provided around a rotary disk 2 at a spacing of 90° while the disk 2 is provided with two bladed parts 5 and two flat parts 6 alternately. A surface 3a facing the rotary disk of each combustor 3 is formed into a part of a circle having its center at a rotary shaft 1. The system is constituted in such a way that when the flat part 6 is situated facing the surface 3a, the flat part 6 covers a combustion gas nozzle 4 in order to close each combustion chamber 8.