A change degree deriving apparatus includes a receiving unit and a deriving unit. The receiving unit is configured to receive first image data of an object including an achromatic color and a first color and reference image data of the object. The first image data relates to the first color. The reference image data serves as a reference. The deriving unit is configured to derive a change degree of the object from a first difference based on the first image data and the reference image data received by the receiving unit. The first difference is a difference between the first image data and the reference image data, which occurs at a chromatic color portion when a portion corresponding to the achromatic color is set as a reference.