To provide a network transmission band changing method and a unit thereof for changing a route in which a band is guaranteed when a fault occurs on a network to another route, and assigning a transmission band thereto.

This network transmission band changing apparatus is established by using a communication system which occupies a predetermined transmission band on a network NT for each communication application AP to be provided from a server 1 to a client terminal 2 on the network NT, and in which a shared band being usable commonly any applications AP using the same routes A or B is prepared; and an admission control apparatus 3 in which the application AP having occupied the predetermined transmission band on the fault route A on the network NT alternatively cuts into an alternate route B, and the value of a transmission band capable of being newly occupied is calculated and changed, including the value of the application AP already occupying the transmission band on the alternate route B, to control the communication system.