A first radio device promotes formation of a temporary group. A second radio device responds to the promotion of the formation of the temporary group. The first radio device includes: a first position information calculator that calculates position information of the first radio device; and a position information transmission controller that controls to transmit the position information of the first radio device to the second radio device at a time of promoting the formation of the temporary group. The second radio device includes: a second position information calculator that calculates position information of the second radio device; a distance calculator that calculates a distance between the first and second radio devices; and a temporary group participation controller that controls to participate in the temporary group when the distance between the first and second radio devices is within a predetermined distance.