Provided is a rotary encoder, including: a rotary scale, which has a predetermined pattern including continuous patterns and a rotational angle original point formed thereon with reference to a pattern center, has a polygonal outer shape, and has the rotational angle original point defined with reference to at least one side of sides of the polygonal outer shape; a hub, which includes projections for abutting the sides of the polygonal outer shape of the rotary scale and positioning the rotary scale; a rotating shaft, which is press-fitted into the hub and rotates coaxially with the pattern center of the rotary scale; and detecting units for irradiating the rotary scale with light and detecting the light reflected by the rotary scale.