1. A face detection method for detecting a face included in an input image by use of at least two inclinations of the face to be detected, wherein a first detection process is performed if the inclination of the face to be detected corresponds to a first inclination where a relatively high face detection probability is expected, and a second detection process having a relatively low face detection probability and a relatively short processing time compared with the first detection process is performed if the inclination of the face to be detected is other than the first inclination.