To provide an eccentricity adjusting device and an eccentricity adjusting method for improving production efficiency and precision by automatically adjusting the eccentricity of a rotation part without stopping the rotation of a rotation part of an object to be adjusted and having a fixing part and the rotation part having an arbitrary eccentricity part and rotating with respect to the fixing part.

An eccentricity detection means 4 for detecting an eccentric part while the rotation part 5a of the object to be adjusted which has the fixing part 5b and the rotation part 5a having the arbitrary eccentric part and rotating with respect to the fixing part 5b and in which a solution member 6 having thermoplasticity is installed on the rotation part 5a is rotated, a light irradiation means 11 solving the solution member 6 and adjusting the eccentric part of the rotation part 5b by irradiating the solution member 6 in the eccentric part with light 11e and a phase adjusting means for adjusting the phase difference θbetween the phase A in the position where the light irradiation means 11 actually irradiates the solution member 6 of the eccentric part and the phase B in the position of the eccentric part are provided.