In the photo-alignment treatment, the substrate is rotated at constant period during UV irradiation, through a sector slit photo mask fixed between the substrate and the light source. In our experiments, a kind of polyimide film was used as the photo-alignment material. The concentric circle of LC orientation, or the radial LC orientation was obtained in the cell over relatively large area, according to whether the direction of sector slit pattern in photo mask. Furthermore, the computer simulation. program is developed from which one can easily predict the molecular orientation pattern obtained by the rotating photo alignment treatment.