A blood vessel lying deep inside a biological tissue can be detected more clearly despite the existence of the biological tissue, particularly, a fat tissue. A biological observation apparatus (1) comprises: a light source unit (4) capable of selectively emitting illumination light beams of two kinds of wavelengths having different absorption intensities with respect to a substance contained in blood an irradiation optical system (7) for irradiating a subject with the illumination light beams from the light source unit (4) a detection optical system (8, 9, 12) for detecting scattered light beams when the subject is irradiated with the illumination light beams of two kinds of wavelengths by the irradiation optical system (7), and acquiring respective images thereof and an image processing section (14) for performing comparison operation processing on the two images acquired by the detection optical system (8, 9, 12).
