An endoscope system 1 includes an illumination unit 42, a light receiving unit 29a having a plurality of pixels arranged in a matrix form, a reading unit 29b for reading pixel signals from the light receiving unit 29a, for each horizontal line, an illumination controller 36 for switching an illumination state of the illumination unit 42 between a first illumination state in which illumination light is emitted, and a second illumination state in which illumination light is not emitted during the reading period, during at least part of the reading period in which the reading unit 29b reads all horizontal lines of the light receiving unit 29a, and a gain adjustment unit 32 multiplying pixel signals by different gain factors for respective horizontal lines to perform gain adjustment, the pixel signals being read during the reading period in which the illumination state of the illumination unit 42 is switched from an illumination state during a previous reading period to the other illumination state.
