To provide an index rotary device capable of performing silent operation in driving, by improving meshing efficiency, by removing a backlash between a cam projection strip part and a driven ball with a simple constitution.

The driven ball 4a can remove the backlash by checking the relative movement between the driven ball 4a and the cam projection strip part 8 due to a constitution for always closely abutting on meshing surfaces 8a and 8b on both sides of the cam projection strip part 8. Thus, the silent operation can be realized without generating a meshing sound of the cam projection strip part 8 and the driven ball 4a in driving, by improving the meshing efficiency of the driven ball 4a and the cam projection strip part 8.