In an authentication apparatus, an input section acquires a living body image which an image capture apparatus generates by capturing an image of a living body that is an object of authentication, and outputs the living body image to an operation section. When the operation section acquires the living body image from the input section, the operation section calculates, on the basis of the living body image acquired and a registered image stored in a registered image storage section, the difference between the relative position of the living body with respect to the image capture apparatus at the time of acquiring the living body image and the relative position of the living body with respect to the image capture apparatus at the time of acquiring the registered image. The output section outputs guidance information for prompting a reduction in the difference in the relative position calculated by the operation section.