The invention provides a biodiagnosis apparatus capable of observing a reflection image of a site other than a fluorescent site through excitation light taken in an observation system so that fluorescence observation can be implemented in good enough color contrast. The apparatus a light source (21), a light source optical system (22), a light transfer system (3) for guiding illumination light from the light source (21) to the living body, an excitation light filter (24) interposed between the light source (21) and the light transfer system (3), an image transfer system for guiding light from the living body to an image plane, and an excitation cut filter (11) located in said image transfer system. The spectral characteristics of illumination light transmitting through the excitation filter (24) and the transmittance characteristics of the excitation cut filter (11) have an overlapping portion. Upon observation of a subject under the biodiagnosis apparatus, the spectral characteristics of a site of the image plane other than a fluorescent site satisfy the following condition: 0.005≦Iλp+Δ/Iλp≦0.5provided that 40≦Δ≦80nm, where λp is the wavelength (nm) at which the spectral intensity reaches a maximum, and I(λp) is indicative of the then spectral intensity.
