A capsule endoscope system, comprising: an illuminating unit including an ordinary light source for illuminating an object by ordinary light of a preset quantity as an ordinary light observation mode and a special light source for illuminating the object by special light of a preset quantity as a special light observation mode; an imaging unit configured to capture an image of the object in each observation mode by receiving reflected light from the object; and a system controller including an exposure time measuring unit configured to measure an exposure time when the imaging unit captures an image in the ordinary light observation mode as brightness information, and an observation mode controller configured to control operations of the ordinary light observation mode for capturing an ordinary light image and the special light observation mode for capturing a special light image, based on the exposure time measured by the exposure time measuring unit, characterized in that the observation mode controller is configured to alternately switch between the ordinary light observation mode and the special light observation mode (S101, S106, S102), and to determine whether the next observation mode is the special light observation mode, if not continue to the ordinary light observation mode, if yes determine whether the exposure time (ΔT2) of the two previous ordinary light observation modes are both successively equal to or more than a specified value (ΔT3), wherein the specified value is smaller than a maximum exposure time setting value (tmax), if no perform the special light observation mode, if yes perform the ordinary light observation mode instead of the special light observation mode. an illuminating unit including an ordinary light source for illuminating an object by ordinary light of a preset quantity as an ordinary light observation mode and a special light source for illuminating the object by special light of a preset quantity as a special light observation mode; an imaging unit configured to capture an image of the object in each observation mode by receiving reflected light from the object; and a system controller including an exposure time measuring unit configured to measure an exposure time when the imaging unit captures an image in the ordinary light observation mode as brightness information, and an observation mode controller configured to control operations of the ordinary light observation mode for capturing an ordinary light image and the special light observation mode for capturing a special light image, based on the exposure time measured by the exposure time measuring unit, characterized in that the observation mode controller is configured to alternately switch between the ordinary light observation mode and the special light observation mode (S101, S106, S102), and to determine whether the next observation mode is the special light observation mode, if not continue to the ordinary light observation mode, if yes determine whether the exposure time (ΔT2) of the two previous ordinary light observation modes are both successively equal to or more than a specified value (ΔT3), wherein the specified value is smaller than a maximum exposure time setting value (tmax), if no perform the special light observation mode, if yes perform the ordinary light observation mode instead of the special light observation mode.