Provided are: an endoscope system which makes it possible to minimize frame rate decline without a reduction in the resolution or brightness of an oxygen saturation image； a processor device for the endoscope system； and a method for operating the endoscope system. During a special observation mode, the present invention captures an image using a CMOS imaging element, by alternatingly irradiating a specimen with first irradiation light and second irradiation light, the latter of which has different spectral characteristics than those of the first irradiation light and includes a different-absorption-wavelength light for which the absorption coefficient differs between oxygenated hemoglobin and reduced hemoglobin, and interposing a non-irradiation period therebetween. The present invention retrieves a first imaging signal from the imaging element during a non-irradiation period following irradiation with the first irradiation light, and retrieves a second imaging signal from the imaging element during a non-irradiation period following irradiation with the second irradiation light. When doing so, the second retrieval time required for retrieval of the second imaging signal is shorter than the first retrieval time required for retrieval of the first imaging signal. The present invention creates an oxygen saturation image on the basis of the first and second imaging signals retrieved from the imaging element.L'invention concerne : un système d'endoscope qui rend possible la réduction au minimum la baisse du taux de trame sans réduction de la résolution ou de la luminosité d'une image de saturation en oxygène； un dispositif de processeur pour le système d'endoscope； et un procédé permettant de faire fonctionner le système d'endoscope. Pendant un mode d'observation spécial, la présente invention capture une image à l'aide d'un élément d'imagerie CMOS, en alternance par l'irradiation d'un spécimen avec une première lumière d'irradiation et une seconde lumière d'irradiatio
