1. An image generation apparatus, comprising: a characteristic point extraction unit configured to extract a characteristic point in an overlapping region of a plurality of component images picked up using a camera built in portable equipment and having pan angles or elevation angles different from each other; a self-position estimation unit configured to estimate three-dimensional coordinate values of the characteristic point and three-dimensional coordinate values of a camera position, which are associated with each other, at the same time in two component images in which the camera positions are displaced from each other; and a synthesis image generation unit configured to adjust, based on the estimated three-dimensional coordinate values of the camera position, the three-dimensional coordinate values of the characteristic point of the component image to correct the component image and combine a plurality of component images having pan angles or elevation angles different from each other to generate a synthesis image.