PURPOSE: To increase the minimum inverting interval and the window width, by mainly using 000, 011, 100 and 110 and auxiliarily using 001 and 110, in converting two binary signal data trains into three binary signal data trains.

CONSTITUTION: The data train of a binary signal is sequentially sectioned into each two data to form an input data block and the data trains are converted into three binary signal data trains in response to four types of data patterns. 100 is taken as the conversion data when the converting data just before the 1st data pattern is 001, 000 is taken when other than 001, 011 is taken when the converting data just before the 2nd data pattern is 000 or 100, 111 is taken when 011 or 111, 000 is taken when the conversion data just before the 3rd data pattern is 110, 111 is taken when other than 110, 001 is taken when the next input data pattern to the 4th pattern is the 1st or 2nd, and 110 is taken as the conversion data when this is the 3rd or 4th.