A data flow amount control device in a mobile communication system which includes a plurality of mobile stations, a control station relaying packets addressed to each of the plurality of mobile stations, and a base station temporarily storing the packets transmitted from the control station in a buffer and transmitting the packets to each of the plurality of mobile stations. The data flow amount control device comprises a determination unit configured to determine an initial value of an amount of packets which are addressed to a mobile station newly starting a communication in the mobile communication system and are transmitted from the control station to the base station, according to the number of mobile stations which are performing the communication in the mobile communication system.