8. A residual stress estimation device for use in suppressing deformation during plastic processing, the residual stress estimation device comprising:

an input unit that receives, in a case where it is assumed that inherent strain is uniformly distributed in one direction in a structure, an input of a measured value related to residual stress measured from a cut piece collected in a region in which the inherent strain is uniformly distributed;

a first estimation unit that estimates a two-dimensional inherent strain distribution in a direction crossing the one direction in the structure based on the measured value received by the input unit;

a second estimation unit that estimates a three-dimensional inherent strain distribution in the structure such that the two-dimensional inherent strain distribution estimated by the first estimation unit continues in the one direction;

a display unit that displays a residual stress estimation result based on the three-dimensional inherent strain distribution estimated by the second estimation unit; and

a processor that optimizes processing conditions of the structure based on the estimated three-dimensional inherent strain distribution to thereby suppress deformation of the structure resulting from the inherent strain.