1. A person retrieval apparatus for retrieving a person on the basis of personal face image information, comprising: an extraction section which extracts personal face image information from images taken by one or more cameras; a position storage section which stores information indicating a priority level of person retrieval processing according to an image-taking position of each camera; a setting section which sets a reliability level to the face image information extracted by the extraction section on the basis of information, stored in the position storage section, indicating the priority level of the person retrieval processing according to the image-taking position of each camera; a memory which stores the face image information extracted by the extraction section and the reliability level set by the setting section in association with each other; and a retrieval section which performs the person retrieval processing on each piece of face image information stored in the memory, in descending order of the reliability level corresponding to each piece of face image information.