For example, a plurality of elliptical candidate areas that become candidate areas of detecting objects are set in an image, characteristic values such as average values of luminance of the pixels inside and outside the set candidate areas are compared, and a candidate area whose difference of the characteristic values is determined to be the maximum is detected as the area of the detecting object. In addition, central moment of the detecting object is calculated, and the inclination of the detecting object in the image is detected based on the calculated central moment. Further, two specific points such as eyes of the driver included in the detecting object are detected, and the inclination of the detecting object in the image determined by the detected two points is detected.