An endoscope system comprising: an illumination unit that is configured to irradiate a test body with first illumination light and second illumination light having a spectral property different from a spectral property of the first illumination light and including different-absorption-wavelength light that has different absorption coefficients for oxygenated hemoglobin and reduced hemoglobin; an endoscope including a CMOS image sensor that is configured to capture an image of the test body illuminated by the illumination unit by using a plurality of pixels arranged in two dimensions in a row direction and in a column direction; and a processor apparatus comprising a controller that is configured to enable a normal observation mode and a special observation mode to be selectively executed, the normal operation mode being a mode in which signal reading from the image sensor is performed in a state where the first illumination light is being emitted from the illumination unit, the special observation mode being a mode in which the first illumination light and the second illumination light are alternately emitted from the illumination unit while a turn-off period is interposed and signal reading from the image sensor is performed during the turn-off period; and an image processor that is configured to generate an oxygen saturation image on the basis of a first image capture signal read from the image sensor during the turn-off period after emission of the first illumination light and a second image capture signal read from the image sensor during the turn-off period after emission of the second illumination light in the special observation mode, wherein the controller is configured to control the image sensor according to a global shutter method in the special observation mode to make a second read time taken to read the second image capture signal shorter than a first read time taken to read the first image capture signal and a sum of the exposure time of the first illumination light and the first read time longer than a frame time in the normal observation mode and a sum of the exposure time of the second illumination light and the second read time shorter than the frame time in the normal observation mode. an illumination unit that is configured to irradiate a test body with first illumination light and second illumination light having a spectral property different from a spectral property of the first illumination light and including different-absorption-wavelength light that has different absorption coefficients for oxygenated hemoglobin and reduced hemoglobin; an endoscope including a CMOS image sensor that is configured to capture an image of the test body illuminated by the illumination unit by using a plurality of pixels arranged in two dimensions in a row direction and in a column direction; and a processor apparatus comprising a controller that is configured to enable a normal observation mode and a special observation mode to be selectively executed, the normal operation mode being a mode in which signal reading from the image sensor is performed in a state where the first illumination light is being emitted from the illumination unit, the special observation mode being a mode in which the first illumination light and the second illumination light are alternately emitted from the illumination unit while a turn-off period is interposed and signal reading from the image sensor is performed during the turn-off period; and an image processor that is configured to generate an oxygen saturation image on the basis of a first image capture signal read from the image sensor during the turn-off period after emission of the first illumination light and a second image capture signal read from the image sensor during the turn-off period after emission of the second illumination light in the special observation mode, wherein the controller is configured to control the image sensor according to a global shutter method in the special observation mode to make a second read time taken to read the second image capture signal shorter than a first read time taken to read the first image capture signal and a sum of the exposure time of the first illumination light and the first read time longer than a frame time in the normal observation mode and a sum of the exposure time of the second illumination light and the second read time shorter than the frame time in the normal observation mode.