1. A vehicle periphery monitoring system comprising: a bird's-eye view image generation section generating bird's-eye view image segments from multiple photographed images photographed to be partially overlapped in a vehicle circumference direction; a boundary indicator addition section adding a boundary indicator indicating a boundary area of the bird's-eye view image segments adjacent each other to an overlapped area of the bird's-eye view image segments; a merger section generating a merged overlapped image by merging mutually overlapped areas of the bird's-eye view image segments according to a preset merger relationship; a displaying bird's-eye view image generation section generating a merged bird's-eye view image containing a boundary-added bird's-eye view image having the boundary indicator and the merged overlapped image as a displaying bird's-eye view image; a displaying section displaying the displaying bird's-eye view image; and a displaying image determination section displaying the merged bird's-eye view image in the displaying section after displaying the boundary-added bird's-eye view image therein.