1. A method of parallelizing codes by processing of a computer, wherein the codes are configured by connecting blocks with internal state and blocks without internal state, the method comprising: creating a graph expression in which nodes represent said blocks and edges represent links between said blocks, and then storing said graph expression in a memory of said computer; grouping said blocks into a plurality of strands by tracing said graph expression in such a manner that every path between the input and output of each of the said strands includes at least one of the said blocks with internal state; selecting a strand having a maximum calculation time from all the said strands; specifying, based on a parent-child relationship among said blocks with internal state and said blocks without internal state, a movable block without internal state in said selected strand having said maximum calculation time; and moving said movable block to an adjacent strand if said calculation time of said strand having said maximum calculation time is shorter after movement of said movable block to said adjacent strand than the calculation time before the movement.