In a blood information measuring apparatus, a plurality of types of light of a superficial layer wavelength set, a middle layer wavelength set, and a deep layer wavelength set are successively applied to a detected hypoxic region. A CCD captures an image under the light of each wavelength set, and an oxygen saturation image is produced independently from one wavelength set to another. A wavelength set determination section creates a histogram of each oxygen saturation image. The wavelength set determination section chooses one of the wavelength sets corresponding to the histogram having a maximum variance as an actual imaging wavelength set. Actual imaging operation is performed using the actual imaging wavelength set, and an oxygen saturation level of each pixel is calculated. The oxygen saturation level is reflected in the image, and the image is displayed on a monitor.