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, otherwise 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, wherein the method is performed using a processor or a computer.