A bandwidth allocation device is included in a communication system having a terminal station device and a terminal device and relaying upstream data, which is received from a communication terminal by a lower device connected to the terminal device, to an upper device connected to the terminal station device. The bandwidth allocation device includes a transmission-permitted period start position determining unit configured to estimate a start position of an arrival period in which the upstream data arrives at the terminal device from the lower device; a transmission-permitted period length determining unit configured to estimate a length of the arrival period based on an amount of upstream data to be transmitted from the lower device to the terminal device; and a bandwidth allocation unit configured to allocate a bandwidth to the terminal device based on the estimated start position and the estimated length of the arrival period.