There is provided a specimen information acquisition apparatus that can obtain an image in which an influence of a local fluence distribution in a specimen is reduced. A signal processing apparatus includes a region extraction unit and an optical constant estimation unit. The region extraction unit extracts two or more regions that have a known absorption coefficient, from an optical characteristic value distribution of the specimen. The optical constant estimation unit estimates an optical constant of a background of the specimen by using optical characteristic values of the two or more regions extracted by the region extraction unit and a local fluence distribution obtained from an optical constant which is set in advance for the specimen background.
