1. A particular-region detection method of detecting particular regions of persons from an image including a plurality of persons as objects, comprising: detecting a region of the image satisfying detection conditions for particular region candidates as a particular region candidate; detecting a face region of a first person and specifying the particular region candidate as a particular region to be detected on condition that the particular region candidate is included in the detected face region; storing face information regarding a face of the first person obtained when the face region is detected; and accessing the face information when a face region of a second person is further detected in the image after said storing of the face information, and detecting the face region of the second person by using the face information as a face detection condition.