An endoscope having: a first light source section adapted to emit white illumination light; a second light source section adapted to emit narrow-band light having a wavelength band narrower than that of the white illumination light, an imaging section adapted to capture a region to be observed by an imaging device having detection pixels of plural colors; and a control section adapted to perform operations of causing the imaging section to output a captured image signal including a return light component of the white illumination light from the region to be observed and a return light component of the narrow-band light from the region to be observed; generating captured images of plural reference colors based on the captured image signal, wherein a first captured image of the captured images contains mostly the return light component of the narrow-band light emitted from the second light source; and changing a brightness level of the first captured image independently from brightness levels of the other captured images, wherein the control section is adapted to perform control such that both the first light source section and the second light source section are turned on simultaneously, and characterized in that the control section is further adapted for dividing the first captured image and a second captured image which has a different reference color from that of the first captured image into common plural image areas; integrating brightness values in each image area of the first captured image to obtain an integrated brightness value of each image area of the first captured image; integrating brightness values in each image area of the second captured image to obtain an integrated brightness value of each image area of the second captured image; obtaining a ratio of (i) the integrated brightness value of each image area of the first captured image and (ii) the integrated brightness value of the image area, having a same image positional relationship with each image area of the first captured image, of the second captured image; extracting image areas, of the first and second captured images, whose ratio is equal to or larger than a threshold value, as characteristic image areas; and selectively changing a brightness level of the characteristic image area of the first captured image. a first light source section adapted to emit white illumination light; a second light source section adapted to emit narrow-band light having a wavelength band narrower than that of the white illumination light, an imaging section adapted to capture a region to be observed by an imaging device having detection pixels of plural colors; and a control section adapted to perform operations of causing the imaging section to output a captured image signal including a return light component of the white illumination light from the region to be observed and a return light component of the narrow-band light from the region to be observed; generating captured images of plural reference colors based on the captured image signal, wherein a first captured image of the captured images contains mostly the return light component of the narrow-band light emitted from the second light source; and changing a brightness level of the first captured image independently from brightness levels of the other captured images, wherein the control section is adapted to perform control such that both the first light source section and the second light source section are turned on simultaneously, and characterized in that the control section is further adapted for dividing the first captured image and a second captured image which has a different reference color from that of the first captured image into common plural image areas; integrating brightness values in each image area of the first captured image to obtain an integrated brightness value of each image area of the first captured image; integrating brightness values in each image area of the second captured image to obtain an integrated brightness value of each image area of the second captured image; obtaining a ratio of (i) the integrated brightness value of each image area of the first captured image and (ii) the integrated brightness value of the image area, having a same image positional relationship with each image area of the first captured image, of the second captured image; extracting image areas, of the first and second captured images, whose ratio is equal to or larger than a threshold value, as characteristic image areas; and selectively changing a brightness level of the characteristic image area of the first captured image.