Body-mounted electronic device system and body-mounted electronic device

A body-mounted electronic device system enabling the user to grasp the conditions of other runners. A master unit and a child unit are mounted on a runner, and a child unit is mounted on another runner. Counting units of the child units count the numbers of steps of the runners at predetermined time intervals, and transmit the data together with their own identification data to the master unit. When the received identification data are in agreement with the identification data stored in an ID setting/storage unit, the reception comparator unit calculates the moving distances of the runners based upon the received step number data, and an among-the-child-units-distance calculation unit calculates the distances among the child units. The distances among the child units that become smaller than a reference distance stored in a preset distance storage unit are notified through a buzzer and a display unit.