An endoscope system includes an image signal processor and external devices connectable to the image signal processor. The external devices include an image output device and a monitor. The image signal processor includes an external device identifier for identifying the external device connected to the image signal processor, a first processing unit, and a second processing unit. The first processing unit processes the image signals to be first processed image signals for generating a first subject image output by the image output device, based on output characteristics data of the identified image output device. The second processing unit processes the image signals to be second processed image signals, based on monitor characteristics data of the identified monitor. The monitor can display a second subject image whose subject is the same as the first subject image, based on the second processed image signals.