An angle detector for detecting an amount of angular change due to the rotation of a rotary body. The angle detector is provided with a rotary body rotating around a rotation axis, a graduated scale having a plurality of graduations along the circumference of the rotary body in a rotation direction, and a plurality of sensors disposed along the circumference. Each of the sensors outputs a signal according to an amount of angular change on the basis of the plurality of graduations. The output signal includes a fundamental wave component having one of the plurality of graduations as a first period first order, and a harmonic wave component having an order that is an integer multiple of at least two times the fundamental wave component. An amount of angular displacement calculated from the output signal includes an angular error component that is due to the harmonic wave component and has an order component that is an integer multiple of the one graduation that is the first period first order. The number of the plurality of sensors is determined on the basis of the number of graduations on the graduated scale and the order component of the angular error component.