Program comparing device and program comparing method

A program comparing device that compares programs described by ladder diagrams, comprising:

• a logical expression converting unit configured to convert a ladder circuit of the program into a logical expression, in units of the ladder circuit;
• an order converting unit configured to rearrange an order of signals of the logical expression of at least one ladder circuit, of two of the ladder circuits that are comparison targets, so as not to change a result of the logical expression;
• and
• a comparing unit configured to compare the logical expression of the one ladder circuit after the order of the signals has been rearranged, with a logical expression of another ladder circuit of the two of the ladder circuits, and judge whether or not the logical expression of the one ladder circuit and the logical expression of the other ladder circuit match.