A group communication system for managing employees, comprising: a first two-way radio configured to be carried by an employee who belongs to an nth (n=1,..., and N) group when the employees are grouped into first to Nth groups; a second two-way radio configured to be carried by an nth manager who manages employees who belong to the nth group; and a third two-way radio configured to be carried by a supervisor who supervises first to Nth managers, 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 and the supervisor, wherein each of the first to third two-way radios (210, 220, 230) 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 who belongs to an nth (n=1,..., and N) group when the employees are grouped into first to Nth groups; a second two-way radio configured to be carried by an nth manager who manages employees who belong to the nth group; and a third two-way radio configured to be carried by a supervisor who supervises first to Nth managers, 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 and the supervisor, wherein each of the first to third two-way radios (210, 220, 230) 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.