1. A computer executable method for analyzing a control flow graph by an abstract interpretation of a program comprising: generating an edge of a control flow graph from a branch instruction to a target address of the branch instruction in an abstract interpretation for an assignment instruction to a branch target variable of a program, the program allocating a particular branch target variable to each of a branch instruction having a plurality of branch targets, the branch target address being loaded from the branch target variable upon branching, a branch address of a branch instruction having one branch target as well as the address assigned by the assignment instruction to the branch target variable being determined as certain constant values determined by compiling the program; adding the target address assigned by the assignment instruction to an object of the abstract interpretation; and terminating a current abstract interpretation in the case that the abstract interpretation reaches to an instruction already subjected to the abstract interpretation.