A collision avoidance assisting system for a vehicle, comprising: a moving object detecting means, which is configured to detect a moving object existing on periphery of the vehicle; a risk estimation means, which is configured to estimate a risk that the moving object detected by said moving object detecting means collides on said vehicle; and an alarmmeans, which is configured to call an attention to a driver of said vehicle, upon basis of the risk of collision estimated by said risk estimation means; characterized by further comprising: a footway boundary detecting means, which is configured to detect a position and a configuration of a footway boundary object on periphery of said vehicle; and a positional relationship analyzing means, which is configured to output at least a relative distance between said moving object and said footway boundary object and a relative distance between said moving object and said vehicle, from position information of the moving object, which is detected by saidmoving object detecting means, and position/configuration information of the footway boundary object, which is detected by said footway boundary object detecting means, whereinsaid risk estimation means estimates the risk of collision between the moving object, which is detected by said moving object detecting means, and said vehicle, at least from the relative distance between said moving object and said footway boundary object, which is outputted from said positional relationship analyzing means, and the relative distance between said moving object and said vehicle, which is outputted from said positional relationship analyzing means. a moving object detecting means, which is configured to detect a moving object existing on periphery of the vehicle; a risk estimation means, which is configured to estimate a risk that the moving object detected by said moving object detecting means collides on said vehicle; and an alarmmeans, which is configured to call an attention to a driver of said vehicle, upon basis of the risk of collision estimated by said risk estimation means; characterized by further comprising: a footway boundary detecting means, which is configured to detect a position and a configuration of a footway boundary object on periphery of said vehicle; and a positional relationship analyzing means, which is configured to output at least a relative distance between said moving object and said footway boundary object and a relative distance between said moving object and said vehicle, from position information of the moving object, which is detected by saidmoving object detecting means, and position/configuration information of the footway boundary object, which is detected by said footway boundary object detecting means, whereinsaid risk estimation means estimates the risk of collision between the moving object, which is detected by said moving object detecting means, and said vehicle, at least from the relative distance between said moving object and said footway boundary object, which is outputted from said positional relationship analyzing means, and the relative distance between said moving object and said vehicle, which is outputted from said positional relationship analyzing means. a footway boundary detecting means, which is configured to detect a position and a configuration of a footway boundary object on periphery of said vehicle; and a positional relationship analyzing means, which is configured to output at least a relative distance between said moving object and said footway boundary object and a relative distance between said moving object and said vehicle, from position information of the moving object, which is detected by saidmoving object detecting means, and position/configuration information of the footway boundary object, which is detected by said footway boundary object detecting means, whereinsaid risk estimation means estimates the risk of collision between the moving object, which is detected by said moving object detecting means, and said vehicle, at least from the relative distance between said moving object and said footway boundary object, which is outputted from said positional relationship analyzing means, and the relative distance between said moving object and said vehicle, which is outputted from said positional relationship analyzing means.