To provide a color wheel which accurately detects rotation and whose manufacturing process can be simplified.

The color wheel 1 is one disc 2 made by combining sector segments 2a, 2b, 2c of different colors. A notch 4 is formed at a portion in contact with the outer periphery of the disc 2 in the boundary of the segments 2a and 2c. A reflection type optical sensor 13 emits light toward the plane of the color wheel 1 from the normal direction, detects presence of the notch 4, and detects rotation of the color wheel 1.