[Solving Means] A signal processing apparatus is a signal processing apparatus for an optical tomographic measurement apparatus that generates measurement light and reference light and measures a tomographic structure of a measurement object on the basis of a signal intensity of interference light between the reference light and return light of the measurement light from the measurement object. An arithmetic unit is configured to calculate a signal intensity of simple reflection among the return light of the measurement light, the simple reflection being one time of reflection at a plurality of layers virtually set in a depth direction from a surface layer side of the measurement object. The arithmetic unit is configured to calculate a signal intensity of multiple reflection on the basis of the signal intensity of the simple reflection, the signal intensity of multiple reflection being a signal intensity of return light generated by being reflected at the plurality of layers three or more times.