In an exposure controller of a camera mounted on a robot for taking an image utilizing incident light from external world in which an object such as a human being is present, a brightness histogram of the image is generated and exposure parameters are set based on the generated histogram. Then, it is determined whether the set exposure parameters are within a predetermined range and when they are out of the range and if a high-brightness imaging region is present in the image due to high-brightness incident light, it is again determined whether it is necessary to remove the high-brightness imaging region. When it is determined to be necessary, the high-brightness imaging region is extracted and is removed from the image, thereby enabling the camera to image the object with suitable brightness even when a bright light source such as the sun is within the camera angle of view.