PURPOSE: To decrease a data storage time for packet-processing a line data of the same destination and same speed and to decrease conversion delay by handling plural lines communicating with a same opposite party equipment as a single line and applying multiplex and packet-processing to the data.

CONSTITUTION: A time division multiplex data/packet conversion section 10 is provided with a 1st channel number rewrite section 3, which rewrites each channel number of a channel having the same destination and same speed read by a 1st data storage means 1 into the same channel number. Moreover, a packet/time division multiplex data conversion section 20 is provided with a 2nd channel number rewrite section 4, which rewrites the same channel number rewritten by the 1st channel number rewrite means 3 into each original channel number. Thus, data of same speed having same destination are multiplexed and processed into packets to reduce the data storage time for packet processing thereby reducing the packet conversion delay.