A medical apparatus comprises a sound-wave radiating member and a light radiating member. The sound-wave radiating member radiates ultrasound wave into an object, the ultrasound wave having a plurality of frequency components different from each other.The light radiating member radiates light into a region within the object, the ultrasound wave being already radiated into the region. Thus, the light reflects and scatters at depth-directional higher-density local portions of the object, which are caused by the ultrasound wave inside the object. Further, the apparatus comprises a light receiving member receiving light reflected in the region in response to the radiated light. In this apparatus, information indicative of a reflected (and scattered) state of the radiated light in the region is calculated based on the received light and the radiated ultrasound wave. For example, the ultrasound wave being radiated increases its frequency over time.
