To provide a circular window operating apparatus which is available for a round window having a circular frame.

According to the circular window operating apparatus, a tilt angle of each operating arm 5 from a fulcrum is changed by an arm rotating means, and a circular block member 4 fixed at a mobile end of each operating arm is operated to open/close a circular opening 3. The arm rotating means is formed of an operating arm rotating portion and a driving means. The operating arm rotating portion is comprised of a plurality of driving arms 6 which are slidably and rotatably connected to operable shaft portions of the operating arms, and each render both ends thereof movable along a peripheral wall in one body with each other. The driving means moves the operating arm rotating portion along the peripheral wall. In this manner, when the operating arm rotating portion is moved along the peripheral wall defining the circular opening by the driving means, the operating arms are simultaneously lifted up and down by the respective driving arms, and therefore the operating arms are rotated, whereby the circular block member is operated to open/close the circular opening.