The endoscope system 1 includes an illumination unit 42, a light receiving unit 29a in which a plurality of pixels are arranged in a matrix, a reading unit 29b that reads pixel signals from the light receiving unit 29a for each horizontal line, and a reading unit 29b that includes all of the light receiving unit 29a. The illumination state of the illuminating unit 42 is set to one of a first illumination state in which illumination light is emitted during at least a part of the readout period for reading out the horizontal line and a second illumination state in which illumination light is not emitted in the readout period. For the pixel signal read in the readout period when the illumination state of the illumination control unit 36 and the illumination unit 42 to be switched is switched from the illumination state in the previous readout period to the other illumination state, the horizontal line A gain adjustment unit 32 that performs gain adjustment by multiplying a different gain coefficient for each is provided.内視鏡システム１は、照明部４２、複数の画素が行列状に配置された受光部２９ａ、受光部２９ａから水平ラインごとに画素信号を読み出す読み出し部２９ｂ、読み出し部２９ｂが受光部２９ａの全ての水平ラインを読み出す読み出し期間の少なくとも一部において照明光を出射させる第１の照明状態と、読み出し期間では照明光を出射させない第２の照明状態と、のいずれかに照明部４２の照明状態を切り替える照明制御部３６、および、照明部４２の照明状態が、一つ前の読み出し期間の照明状態から他方の照明状態に切り替えられた読み出し期間に読み出された画素信号に対しては、水平ラインごとに異なるゲイン係数を乗じることによりゲイン調整を行うゲイン調整部３２を備える。
