To reduce the processing load on a processor when changing an assigned band quantity in a network system having a band management device which manages an assigned band to each transmission/reception system by a table.

A first table where ID numbers of transmission devices which are permitted to send a packet are described, a second table where ID numbers of transmission devices which are permitted to send a packet are described in a combination different from that of the first table, and a third table where pointer information indicating whether the first table or the second table should be referred to is described are provided, and the first table or the second table is determined as a table to be referred to in each stage of the third table by pointer information of the third table, and transmission devices of the ID numbers which are described in the referred table are permitted to send a packet to the network to manage a band quantity for use of each transmission/reception system in the network, and the assigned band is changed by rewriting pointer information the third table.