A capsule medical apparatus (10) in an in-vivo information acquisition system (1) includes an illumination unit (13) that illuminates an inside of the subject (100); an imaging unit (12) having an effective pixel region (R eff ) on which an optical image of the inside of the subject (100) illuminated by the illumination unit (13) is formed and an optical black region (R OB ) at which the optical image is shielded; and a light adjustment control unit (16, 17, 18) that adjusts an amount of light from the illumination unit (13) based on pixel values of the effective pixel region (R eff ) of an image signal and pixel values of the optical black region of the image signal (R OB ).