To provide an angle determination accuracy measuring device and an angle determination accuracy measuring method capable of easily performing angle determination accuracy measurement of a rotational moving shaft, shortening measurement time, and reducing costs.

The angle indexing accuracy measuring device 10 including an encoder 11, an attachment shaft 12 having an outer diameter shape and a length corresponding to the magnitude of sliding resistance of the encoder 11, and a computation part calculating a correction value measures the angle determination accuracy of the rotational moving shaft 13.