Resin inspection method and resin inspection apparatus

A resin inspection method for inspecting a resin material containing a recycled material or a molded product made of the resin material as an inspection target, the method comprising:

• acquiring a spectral characteristic value at a light absorption wavelength of the inspection target;
• and
• estimating a degree of deterioration of the recycled material contained in the inspection target based on the spectral characteristic value of the inspection target,
• wherein estimating the degree of deterioration includes:
• calculating a first regression line corresponding to a content of the recycled material of the inspection target and representing a correlation between the spectral characteristic value and the degree of deterioration based on a correlation database containing multiple pieces of correlation data in each of which the spectral characteristic value, the degree of deterioration of the recycled material, and the content of the recycled material in the resin material are associated with each other and in which at least the degrees of deterioration differ from each other, and
• calculating the degree of deterioration corresponding to the spectral characteristic value of the inspection target based on the first regression line.