A band limiter comprises an optical filter, which has first and second filter sections, and a filter moving mechanism for moving the optical filter to place the first or second filter section in a light path of blue light. A passband where transmittance of the first filter section is greater than or equal to half a peak value thereof is defined as a first transmission band. The first transmission band includes a peak wavelength, at which an absorption coefficient of hemoglobin is at its peak. A passband where transmittance of the second filter section is greater than or equal to half a peak value thereof is defined as a second transmission band. The second transmission band does not include an isosbestic wavelength (in the order of 450 nm), at which an absorption coefficient of oxyhemoglobin equals or crosses an absorption coefficient of deoxyhemoglobin.
