First, a first narrow band light having a wavelength different in absorbance between the first characteristic substance (14) and the second characteristic substance (16) contained in the target site (12) which is the desired observation target 24) and the second narrow band light (28) are selected (step S1). The first narrowband light and the second narrowband light are applied to the object to be observed (step S2), and the reflected light of the first narrowband light from the object to be observed and the second narrowband light The reflected light is imaged (step S3). Then, based on the imaging data obtained by the imaging, a characteristic substance presence image representing the presence of the first characteristic substance and the second characteristic substance is generated (step S4) and displayed (step S5) .まず、所望の観察対象物である注目部位（１２）に含まれる第１の特徴物質（１４）と第２の特徴物質（１６）とで互いに吸光度の異なる波長を持つ第１の狭帯域光（２４）と第２の狭帯域光（２８）とが、選択される（ステップＳ１）。これら第１の狭帯域光と第２の狭帯域光とが、観察対象物に照射され（ステップＳ２）、観察対象物からの第１の狭帯域光の反射光と第２の狭帯域光の反射光とが、撮像される（ステップＳ３）。そして、これら撮像により得られた撮像データに基づいて、第１の特徴物質と第２の特徴物質の存在を表す特徴物質存在画像が、生成されて（ステップＳ４）、表示される（ステップＳ５）。
