According to an embodiment of the present application, there is provided a medical apparatus, including: a light source unit configured to be capable of emitting light including at least natural emission light, the light being guided into an optical probe; a first detecting unit configured to detect an intensity of light exiting from the light source unit; and a calculation unit configured to calculate to approximate to a non-linear function based on an intensity of light detected by the first detecting unit for calibration of the optical probe.