A damage evaluation device includes: a phased array probe that irradiates an ultrasonic signal from a surface of an inspection metal toward an inside of the inspection metal and detects a reflection signal reflected in a predetermined region inside the inspection metal; and an arithmetic processor. The arithmetic processor sets planes parallel to each other in an inspection region, calculates pixel data by quantifying the reflection signal from segments set in each of the planes; calculates a scattering degree of the pixel data, and evaluates damage of the inspection metal based on the scattering degree.