According to the present invention: a phase gradient calculating unit calculates a phase gradient on a plane intersecting the light radiation direction of an optical coherence tomography signal representing the state of a specimen, for each sample point arranged on the plane; and for each of a plurality of routes from a starting point, which is a sample point of which the bulk phase error has been determined, to an end point, which is a sample point of which the bulk phase error has not been determined, a bulk phase error calculating unit integrates the phase gradient at each sample point along each route to calculate a route-specific phase error at the end point, and defines the bulk phase error at the end point by combining the route-specific phase errors between the plurality of routes.
SIGNAL PROCESSING DEVICE, SIGNAL PROCESSING METHOD, AND SIGNAL PROCESSING PROGRAM