An object observing apparatus, comprising: a reference light intensity information storage unit configured to store reference light intensity information, which is information regarding a light intensity at each light-receiving probe, and is information used as a reference; a light intensity information acquiring unit that, using a near-infrared measurement apparatus having at least one probe set consisting of a pair of a light-transmitting probe for transmitting light to an object that is to be observed and a light-receiving probe for receiving light, is configured to acquire light intensity information, which is information regarding a light intensity of light received by each light-receiving probe, in a case where light with a certain light intensity is transmitted from each light-transmitting probe forming each probe set to the object; a light intensity change information acquiring unit that is configured to acquire, for each probe set, light intensity change information, which is information regarding a light intensity change, from the reference light intensity information in the reference light intensity information storage unit and the light intensity information acquired by the light intensity information acquiring unit; an estimating unit that is configured to acquire optical characteristic-changed region information, which is three-dimensional information regarding a position with a light absorbance change inside the object, using the light intensity change information for each probe set; and an output unit that is configured to output the optical characteristic-changed region information acquired by the estimating unit; wherein the estimating unit, in which sensitivity information, which is information indicating a relationship between an optical characteristic change and a light intensity change, is stored, is configured to perform correction according to sensitivity attenuation in accordance with a depth, using the sensitivity information, and to introduce sparseness for improving a space resolution, thereby acquiring the optical characteristic-changed region information. a reference light intensity information storage unit configured to store reference light intensity information, which is information regarding a light intensity at each light-receiving probe, and is information used as a reference; a light intensity information acquiring unit that, using a near-infrared measurement apparatus having at least one probe set consisting of a pair of a light-transmitting probe for transmitting light to an object that is to be observed and a light-receiving probe for receiving light, is configured to acquire light intensity information, which is information regarding a light intensity of light received by each light-receiving probe, in a case where light with a certain light intensity is transmitted from each light-transmitting probe forming each probe set to the object; a light intensity change information acquiring unit that is configured to acquire, for each probe set, light intensity change information, which is information regarding a light intensity change, from the reference light intensity information in the reference light intensity information storage unit and the light intensity information acquired by the light intensity information acquiring unit; an estimating unit that is configured to acquire optical characteristic-changed region information, which is three-dimensional information regarding a position with a light absorbance change inside the object, using the light intensity change information for each probe set; and an output unit that is configured to output the optical characteristic-changed region information acquired by the estimating unit;