1. A person image retrieval apparatus which retrieves an image in which the same person shown in a retrieval target image is shown, from a group of search target images, the person image retrieval apparatus comprising: a search target detection section which detects number of images of the group of search target images; a comparison target setting section which sets face parts to be compared based on the number of images of the group of search target images detected by the search target detection section, the comparison target setting section setting fewer face parts to be compared as the number of images of the group of search target images is larger; a comparison/determination section which compares the face of the person shown in the retrieval target image and the face of the person shown in each image of the group of search target images by the parts set by the comparison target setting section and determines an image with a particular correlation to be a similar image; and an output section which outputs the image determined by the comparison/determination section to be a similar image on a display device.