A polarizer of the present invention comprises an azo compound which is represented by the following general formula (I). In the general formula (I), Q.sub.1 represents an optionally substituted aryl group, Q.sub.2 represents an optionally substituted arylene group, M represents a counter ion, l represents an integer of from 1 to 6, and m represents an integer of from 0 to 5 (l+m.ltoreq.6). ##STR00001##