1. A group analysis system comprising a plurality of sensor terminals and a controller connected to said plural sensor terminals, wherein each of said sensor terminals has a first sensor to acquire relative position information on a person carrying said sensor terminal and a second sensor to acquire environmental information on said person carrying said sensor terminal, and wherein said controller has an input-output unit to acquire said relative position information and said environmental information transmitted from said each of said sensor terminals, and an analyzer to detect an initial group of said sensor terminals with said relative information, extract the feature quantity, showing the environment of a site, of said initial group from said environmental information on each of said sensor terminals constituting said initial group, extract the feature quantity showing the environment of a site from said environmental information on said sensor terminal not belonging to said initial group, and decide a group to which said sensor terminal not belonging to said initial group belongs by comparing said feature quantity of said initial group with said feature quantity of said sensor terminal not belonging to said initial group.