By running the internal observation it is arranged to detect the backscattered light irradiating illumination light to the small area of the surface (living tissue, for example) a subject with light scattering, to be larger than the illuminated area to the area of the detection region The internal observation device such as an endoscope to increase the amount of detected light in the configuration simple and inexpensive, and can shorten the time required for detection of (eg, a blood vessel) the object to be observed, can detect deep regions conventionally are provided.光散乱性を有する対象(例えば生体組織)表面の微小面積に照明光を照射しその後方散乱光を検出するようにした内部観察を実行し、検出領域の面積を照明領域よりも大きくすることにより、簡便かつ安価な構成で検出光量を増やし、観察すべき物体(例えば血管)の検出に要する時間を短縮したり、従来より深い領域を検出できる内視鏡等の内部観察装置が提供される。
