PURPOSE: To enable a communication between terminals which have different terminal attributes by providing a storage means for data, a transmission rate conversion part, a connection control part which has a rate converting function for the transmission rate conversion part and a call connection retrial processing function at the time of incoming rejection due to transmission rate mismatching.

CONSTITUTION: When a terminal 3b sends a request for call setting to a terminal 3b through a terminal adapter 1b while the terminals 3a and 3b differ in terminal attribute such as a transmission rate, etc., and there is no influence upon an end-end communication except the difference in transmission rate, a terminal adapter device 1a receives and recognizes terminal attribute information on the terminal 3b by a connection control part 6 as well call setting information. Then the transmission rate conversion part 7 sets a mode wherein data is set and received to and from the transmission line to a communication controller 2 at the transmission rate of the terminal 3b. At this time, even if the transmission rate of the originating terminal 3b is faster, the data is stored in a buffer, etc., by providing the buffer to the transmission rate conversion part 7. Further, when the terminal 3a sends a request for call setting to the terminal 3b reversely, the connection control part 6 analyzes the cause of incoming call rejection due to terminal attribute mismatching once receiving the rejection from the terminal 3b. Then the mode of the transmission rate conversion part 7 is set similarly and reconnection trial processing for outputting the request for call setting again is performed.