In order to solve a problem that a local optical characteristic-changed region inside an object cannot be accurately estimated, an object observing apparatus includes: a light intensity information acquiring unit that acquires light intensity information received by each light-receiving probe in a case where light with a certain light intensity is transmitted from each light-transmitting probe of a near-infrared measurement apparatus to an object a light intensity change information acquiring unit that acquires, for each probe set, light intensity change information regarding a light intensity change, from reference light intensity information and light intensity information an estimating unit that acquires three-dimensional optical characteristic-changed region information regarding a position with a light absorbance change inside the object, using the light intensity change information and an output unit that outputs the optical characteristic-changed region information wherein the estimating unit includes: a correcting part that performs correction according to sensitivity attenuation in accordance with a depth, using sensitivity information and a sparseness applying part that introduces sparseness for improving a space resolution, thereby acquiring the optical characteristic-changed region information. Accordingly, it is possible to accurately estimate, as three-dimensional information, a local optical characteristic-changed region inside an object.
