In a communication of explicit multicast system used in SICC, the frequency of variation of the transmission rate is reduced to achieve a multimedia data transmission exhibiting a high quality. An available bandwidth estimating part (102) of a transmitting apparatus (100) uses feedback information, which is received by a receiving part (101) from a receiving apparatus (200), to estimate a bandwidth available to the receiving apparatus. A bandwidth correcting part (103) corrects, based on a difference in header size between a current class and an upper-order class, the estimated available bandwidth. A class deciding part (104) uses the corrected bandwidth to change the class to which the receiving apparatus belongs.