A group communication system for managing employees (E), comprising: a first two-way radio configured to be carried by an employee (E) who belongs to an nth (n=1, ..., and N) group when the employees (E) are grouped into first to Nth groups; a second two-way radio configured to be carried by an nth manager (M) who manages employees (E) who belong to the nth group; and a third two-way radio configured to be carried by a supervisor (S) who supervises first to Nth managers (M), wherein an nth unique code is assigned to the nth group, and an (N+1)th unique code is assigned to an (N+1)th group which comprises the first to Nth managers (M) and the supervisor (S), wherein each of the first to third two-way radios comprises a first push-to-talk, PTT, button and a second PTT button , and is configured to transmit a voice packet comprising at least one unique code set corresponding to the first PTT button while the first PTT button is pushed, transmit a voice packet comprising at least one unique code set corresponding to the second PTT button while the second PTT button is pushed, and process and output a received voice packet when the received voice packet comprises at least one unique code set corresponding to a reception group, wherein in the first two-way radio , the nth unique code is set corresponding to the first PTT button or the second PTT button , and the nth unique code is set corresponding to the reception group, and wherein in the second two-way radio , the nth unique code is set corresponding to the first PTT button , the (N+1)th unique code is set corresponding to the second PTT button , and the nth unique code and the (N+1)th unique code are set corresponding to the reception group. a first two-way radio configured to be carried by an employee (E) who belongs to an nth (n=1, ..., and N) group when the employees (E) are grouped into first to Nth groups; a second two-way radio configured to be carried by an nth manager (M) who manages employees (E) who belong to the nth group; and a third two-way radio configured to be carried by a supervisor (S) who supervises first to Nth managers (M), wherein an nth unique code is assigned to the nth group, and an (N+1)th unique code is assigned to an (N+1)th group which comprises the first to Nth managers (M) and the supervisor (S), wherein each of the first to third two-way radios comprises a first push-to-talk, PTT, button and a second PTT button , and is configured to transmit a voice packet comprising at least one unique code set corresponding to the first PTT button while the first PTT button is pushed, transmit a voice packet comprising at least one unique code set corresponding to the second PTT button while the second PTT button is pushed, and process and output a received voice packet when the received voice packet comprises at least one unique code set corresponding to a reception group, wherein in the first two-way radio , the nth unique code is set corresponding to the first PTT button or the second PTT button , and the nth unique code is set corresponding to the reception group, and wherein in the second two-way radio , the nth unique code is set corresponding to the first PTT button , the (N+1)th unique code is set corresponding to the second PTT button , and the nth unique code and the (N+1)th unique code are set corresponding to the reception group. <EOS>