PURPOSE: To stop quickly the generation of a signal from a device (a) by storing temporarily a signal generated from the device (a) in a network A of the CSMA/CD system in case transmitting the said signal to a certain device (b) of other betwork B or directly to the device (b), and transmitting a signal from the converter when the storage exceeds the storage capacity of the storage means or is on the verge of exceeding, causing the collision of signals supplied from the device (a).

CONSTITUTION: A signal 40 from an MODEM is confirmed for the normal procedure by a transmission procedure detecting circuit 41 and fed to an error detection circuit 42. An informing signal part 44 is fed to a buffer memory. A signal stored in the buffer memory from the network B goes to a transmission signal 54 to the network A, fetched by a word assembling circuit 48, grouped into blocks, added with a check bit for error detection and fed to the MODEM through a transmission procedure transmitting circuit 29. When an overflow signal 56 of the buffer memory arrives from a control signal, a collision forcing signal generating circuit 58 is set, the transmission request is outputted and also a collision forcing signal is fed to a word assembling circuit 48. The MODEM of the terminal (a) detects collision and stops transmission.