1. A personal authentication apparatus comprising: a facial region extraction unit configured to extract an image of a facial region of a person obtained from image sensing input unit; a guide unit configured to guide motion of the person of interest; a feature amount extraction unit configured to extract a feature amount of a face from the image of the facial region extracted by the facial region extraction unit while the motion is guided by the guide unit; and a unit configured to authenticate the person of interest in accordance with a similarity between the feature amount extracted by the feature amount extraction unit, and a feature amount which is registered by dictionary registration unit that has registered a feature amount of the person of interest in advance.