An imaging-device driving unit comprising a detector and an exposure controller is provided. The imaging-device driving unit controls a CMOS imaging device amounted in an endoscope. The detector detects the pattern of emitted illumination light. The illumination light is emitted by a light source. The illumination light is shone on a subject. The CMOS imaging device is ordered to capture an optical image of the subject. The exposure controller orders the CMOS imaging device to perform the global exposure and the line exposure when the patterns of emitted illumination light detected by the detector are the first and second patterns, respectively.