A signal detector for use in the digital signal communication, comprising a tentative decision means for assigning certain symbols to receiving signals based on a predetermined value; a first memory means for storing the output of said tentative decision means in sequence; a second memory means for storing a plurality of reference values prepared in association with all the signals to be received, said signals corresponding to the symbol sequence assigned by said first memory means; a selection means for selecting at least one of said reference values based on at least a part of the contents of said first memory; and a processing means wherein there is proceeded by using said selected reference value the process to relate said receiving signals with signals to be received that are most likely receiving signals among all the signals to be received, thereby producing output.