To automatically respond to a different transmission medium and an external noise source and also to minimize a distortion by responding to detection of the characteristic of a transmitting signal and adjusting transition speed such as rising speed or the falling one.

A circuit 22 is connected with a link 12 as shown by the figures of one or multiple connecting points 24a, 24b or 24c. The circuit 22 feeds-back the parameter characteristic of the transmitting signal to an interface 16c. The interface 16c permits a processor 16a to utilize the information in order. When feed-back information is received, the processor 16a adjusts one or multiple parameters in the transmitting signal on the link 12. Therefore, rising speed and falling speed are adjusted so that a control element 16 is optimized in transmission quality on the link 12 at prescribed transmission speed.