An endoscopic diagnosis system, comprising: a white light source (LD2, 54A, 54B) for emitting white light; a first narrowband light source for emitting first narrowband light having a given wavelength range; a second narrowband light source for emitting second narrowband light having a wavelength range different from that of the first narrowband light; a light source controller for controlling on-off actions and light amounts of the white light source, the first narrowband light source and the second narrowband light source, respectively; an image sensor for receiving reflected light from a subject illuminated with the white light to acquire a normal light image in a normal light observation mode, receiving reflected light from the subject illuminated with the white light and the first narrowband light emitted at a first emission ratio toward the subject to acquire a narrowband light image for blood vessel observation in a narrowband light observation mode, and receiving reflected light from the subject illuminated with the second narrowband light emitted toward the subject to acquire a narrowband light image for oxygen saturation level observation in an oxygen saturation level observation mode; a controller for switching between the narrowband light observation mode and the oxygen saturation level observation mode alternately in this order to control such that the narrowband light image for blood vessel observation and the narrowband light image for oxygen saturation level observation are acquired alternately in a time-sharing manner; an image processor for calculating an oxygen saturation level of blood hemoglobin of the subject based on the narrowband light image for blood vessel observation and the narrowband light image for oxygen saturation level observation to generate an oxygen saturation level image showing a distribution of the oxygen saturation level; and a display unit for simultaneously displaying the narrowband light image for blood vessel observation and the oxygen saturation level image. a white light source (LD2, 54A, 54B) for emitting white light; a first narrowband light source for emitting first narrowband light having a given wavelength range; a second narrowband light source for emitting second narrowband light having a wavelength range different from that of the first narrowband light; a light source controller for controlling on-off actions and light amounts of the white light source, the first narrowband light source and the second narrowband light source, respectively; an image sensor for receiving reflected light from a subject illuminated with the white light to acquire a normal light image in a normal light observation mode, receiving reflected light from the subject illuminated with the white light and the first narrowband light emitted at a first emission ratio toward the subject to acquire a narrowband light image for blood vessel observation in a narrowband light observation mode, and receiving reflected light from the subject illuminated with the second narrowband light emitted toward the subject to acquire a narrowband light image for oxygen saturation level observation in an oxygen saturation level observation mode; a controller for switching between the narrowband light observation mode and the oxygen saturation level observation mode alternately in this order to control such that the narrowband light image for blood vessel observation and the narrowband light image for oxygen saturation level observation are acquired alternately in a time-sharing manner; an image processor for calculating an oxygen saturation level of blood hemoglobin of the subject based on the narrowband light image for blood vessel observation and the narrowband light image for oxygen saturation level observation to generate an oxygen saturation level image showing a distribution of the oxygen saturation level; and a display unit for simultaneously displaying the narrowband light image for blood vessel observation and the oxygen saturation level image.