There is provided a method for transmitting data to a multicast group including a plurality of receivers by using an X-cast mode, comprising the steps of transmitting an X-cast IP data packet having a X-cast header including addresses of a destination router and the multicast group, wherein the destination router is connected to the receivers, converting the X-cast IP data packet to a multicast IP data packet in the destination router and sending the multicast IP data packet to the receivers, wherein an IP header of the multicast IP data has the address of the multicast group. The source router can transmit an IP data packet to a multicast group having a medium or large number of receivers by using the X-cast mode.