A modulo N calculating method for an M1*M2-bit binary integer, wherein N, M1 and M2 are integers, includes the steps of dividing the M1*M2-bit binary integer into M1 bits and performing AND operation on each M1 bits and a specific binary integer; and changing a value of an output register depending on the AND operation result and storing the value thereto. A modulo N calculating apparatus includes an input unit for receiving an M1*M2-bit binary integer, wherein N, M1 and M2 are integers; and an AND operation unit for performing AND operation on the M1*M2-bit binary integer and a specific binary integer. Furthermore, when the M1 and the N may be 4 and 3, respectively, the specific binary value may be 1010 or 0101.