Radiation is captured without fail, and a sharp image of a region where radiation is generated is acquired. A capsule medical device (3) includes an excitation light source (7) that generates excitation light for irradiating an inner wall (4) of a body cavity, a CCD (9), having variable sensitivity, that captures fluorescence generated at the inner wall (4) of the body cavity by the excitation light emitted from the excitation light source (7) to acquire a two-dimensional fluorescence image, and a control unit (35) that performs control so as to reduce the sensitivity of the CCD (9) when the fluorescence intensity in at least part of the fluorescence image acquired by the CCD (9) exceeds a predetermined threshold.
