The purpose of the present invention is to detect fat stably while maintaining smooth observation in the case where the amount of blood placed on the fat is small and while improving the accuracy of the detection of blood when blood is placed on the fat. A living body observation device (1) equipped with a light source section (3) for irradiating a biological tissue with illuminating light, an imaging section (11) for imaging reflected light in the biological tissue to acquire an image, a fat detection section for detecting fat in the acquired image, a blood detection section for detecting blood in the image, and a control section (16) for controlling the light source section (3) and/or the imaging section (11) on the basis of the detection results obtained by the fat detection section and the blood detection section, wherein the control section (16) makes it possible to switch between a simultaneous-type first imaging mode in which multiple light beams having different wavelength bands from each other are imaged simultaneously and a frame sequential-type second imaging mode in which the light beams are imaged sequentially, depending on the condition of blood detected in the image by the blood detection section when fat is detected in the image by the fat detection section.Le but de la présente invention est de détecter de manière stable la matière grasse tout en maintenant la facilité dobservation dans le cas où la quantité de sang placé sur la matière grasse est faible et tout en améliorant la précision de la détection de sang quand le sang est placé sur la matière grasse. Linvention concerne un dispositif dobservation dun corps vivant (1) équipé dune section de source de lumière (3) pour irradier un tissu biologique avec une lumière déclairage, une section dimagerie (11) pour imager la lumière réfléchie dans le tissu biologique pour acquérir une image, une section de détection de matière grasse pour détecter la matière grasse dans limage acquise, une section de d
