In reliable multicast communications, lost information due to packet loss should be re-multicasted. NAK-based retransmission scheme is said to be effective for scalable reliable multicast communications because it can avoid implosion of control packets. When the source sends packets faster than receiver's ability, packet loss due to buffer overflow occurs constantly at corresponding receivers. With this constant packet loss, implosion of control packets degrades total throughput seriously even in the case of NAK-based retransmission scheme. In order to prevent this kind of constant packet loss at receivers, flow control scheme should be implemented for reliable multicast communications. In the paper, we propose a new flow control scheme suitable for NAK-based retransmission scheme. From the viewpoint of flow control, receiving a NAK indicates that transmission rate is too high. However, in multicast communications, multiple NAKs may be generated for a corresponding packet. If the transmission rate is decreased simly by receiving a NAK, the rate may be decreased excessively. In the paper, logging information of transmission rate stored at the sender is proposed to be effective to prevent the transmission rate. Performance evaluation by computer simulation shows that the proposed scheme notably improves throughput performance compared with the case of no flow control.