1. A road surface undulation estimation device, which is configured to input a vehicle periphery image captured by a camera, the camera being installed on a vehicle traveling on a road surface so as to be capable of capturing an image of a periphery of the vehicle, the road surface undulation estimation device comprising: a storage unit configured to store camera installation information acquired in advance; an object detection unit configured to detect regularly appearing objects installed at a constant installation interval on the road surface from the vehicle periphery image captured by the camera, calculate positions of the respective detected regularly appearing objects in the vehicle periphery image, and output a calculation result as position information; a position transformation unit configured to transform, based on the position information input from the object detection unit and the camera installation information acquired from the storage unit, the positions of the respective regularly appearing objects in the vehicle periphery image into positions of the respective regularly appearing objects in a real space, and output a transformation result as detection positions of the respective regularly appearing objects; and a road surface estimation unit configured to calculate respective detection intervals between neighboring detection positions out of the respective detection positions input from the position transformation unit, and estimate, from the respective detection positions, the respective calculated detection intervals, and the constant installation interval of the regularly appearing objects, inclinations of an actual road surface with respect to a road surface obtained through the transformation calculation by the position transformation unit.