A blood information measuring apparatus comprising: a lighting section for applying illumination light to an internal body portion having a blood vessel; an imaging section for performing photoelectric conversion of reflected light from said internal body portion irradiated with said illumination light and outputting an image signal; a wavelength band chanting element for changing a wavelength band of said illumination light to be applied to said internal body portion or said reflected light to be incident on said imaging section in accordance with one of plural wavelength sets; a blood information calculation section for calculating blood information of blood flowing through said blood vessel based on said image signal; a comparison section for comparing said calculated blood information with a threshold value; a wavelength set switching section for controlling said wavelength band changing element so as to switch among said plural wavelength sets in accordance with a comparison result of said comparison section, each of said wavelength sets including plural types of narrow band light that penetrate to similar depths into said internal body portion; and a monitor for displaying said blood information measured with each of said wavelength sets, wherein said blood information is an oxygen saturation level of hemoglobin calculated based on absorbance, said wavelength set switching section is configured to choose one of said plural wavelength sets as an abnormality detection wavelength set used for detection of an abnormal region; when said oxygen saturation level measured with said abnormality detection wavelength set is less than said threshold value, said comparison section outputs an abnormal region detection signal; and said wavelength set switching section is configured to switch in response to said abnormal region detection signal from said abnormality detection wavelength set to one of said other wavelength sets, to measure said oxygen saturation level of said blood flowing through said blood vessel at a different depth. a lighting section for applying illumination light to an internal body portion having a blood vessel; an imaging section for performing photoelectric conversion of reflected light from said internal body portion irradiated with said illumination light and outputting an image signal; a wavelength band chanting element for changing a wavelength band of said illumination light to be applied to said internal body portion or said reflected light to be incident on said imaging section in accordance with one of plural wavelength sets; a blood information calculation section for calculating blood information of blood flowing through said blood vessel based on said image signal; a comparison section for comparing said calculated blood information with a threshold value; a wavelength set switching section for controlling said wavelength band changing element so as to switch among said plural wavelength sets in accordance with a comparison result of said comparison section, each of said wavelength sets including plural types of narrow band light that penetrate to similar depths into said internal body portion; and a monitor for displaying said blood information measured with each of said wavelength sets, wherein said blood information is an oxygen saturation level of hemoglobin calculated based on absorbance, said wavelength set switching section is configured to choose one of said plural wavelength sets as an abnormality detection wavelength set used for detection of an abnormal region; when said oxygen saturation level measured with said abnormality detection wavelength set is less than said threshold value, said comparison section outputs an abnormal region detection signal; and said wavelength set switching section is configured to switch in response to said abnormal region detection signal from said abnormality detection wavelength set to one of said other wavelength sets, to measure said oxygen saturation level of said blood flowing through said blood vessel at a different depth.