An endoscope system includes a light source, a scope, a detector, an adjuster, and a tool. The light source emits illuminating light to illuminate a subject. The scope transmits the illuminating light for emission from the end of the scope. The detector detects the luminance and/or chromaticity of an entering light that enters the scope. The adjuster adjusts the light amount and/or white balance of the illuminating light, based on the luminance and/or chromaticity of the entering light. The end of the scope is inserted into the tool. The tool includes a reflecting member that reflects the illuminating light emitted from the end of the scope so as to become the entering light. The distance between the end of the scope that is inserted into the tool and the reflecting member is adjustable.