1. A vehicular periphery monitoring apparatus configured to monitor a periphery of a vehicle according to an image acquired from a single imaging device mounted in the vehicle to denote the periphery of the vehicle, comprising: a first processing element configured to set a region in the image where an object is present as an object region; and a second processing element configured to calculate a change rate of the size of the object region between two times separated by a specified interval equivalent to a standard motion cycle or a half motion cycle of the object and determine a distance from the vehicle to the object according to the specified interval and the change rate of the size of the object region.