1. A data flow analyzing apparatus comprising: an analysis rule storage which stores analysis rules having definitions of data types; a data flow analyzer which performs data flow analysis on an analysis target program as a target of analysis by using the analysis rules stored in the analysis rule storage to thereby output unsafe data-including procedures as detected points; an analysis rule candidate generator which generates candidates of analysis rules based on the detected points; and an analysis rule candidate output which outputs the analysis rule candidates generated by the analysis rule candidate generator to a predetermined output.