1. A road surface undulation estimation device, which is configured to input a vehicle periphery image captured by a camera to capture an image of a periphery of the vehicle, the road surface undulation estimation device comprising: a storage to store camera installation information in advance; an object detector to detect regularly appearing objects installed at a constant installation interval on a 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 result of the calculated positions as position information; a position transformer configured to transform, based on the position information input from the object detector and the camera installation information input from the storage, 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 result of the transformed positions as detection positions of the respective regularly appearing objects; and a road surface estimator to obtain a plurality of first straight lines passing through a lens center of the camera and the respective detection positions, obtain a second straight line that intersects with each of the plurality of first straight lines at the installation interval of the regularly appearing objects, determine the second straight line as an actual road surface, calculate respective detection intervals between neighboring detection positions of the respective detection positions input from the position transformer, determine a third straight line connecting the respective detection positions as a detected road surface, and determine an inclination angle between the actual road surface and the detected road surface, wherein the object detector, the position transformer, and the road surface estimator are included in one or more computing units.