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 display 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 bird's-eye view image for display; a displaying section displaying the bird's-eye view image for display; and a display 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, wherein in a display switchover process from g, of the boundary-added bird's-eye view to displaying of the merged bird's-eye view image as the displaying bird's-eye view image, displaying is switched over to displaying of the merged overlapped image progressively and concentrically from vicinity of the vehicle.