A ladder diagram program creation assistance device, comprising: a partial circuit selector, configured to select a partial circuit comprising a plurality of contacts (a, b, c, A) in a ladder diagram program and appearing more than a predetermined number of times; a replacement circuit generator, configured to generate a replacement circuit comprising a smaller number of contacts (a, b, c, A) than the partial circuit selected by the partial circuit selector; an auxiliary circuit generator, configured to generate an auxiliary circuit that causes the replacement circuit generated by the replacement circuit generator to perform a same action as the partial circuit selected by the partial circuit selector; and a program editor, configured to perform, on the ladder diagram program, a replacement process for replacing a partial circuit appearing in the ladder diagram program with the replacement circuit generated by the replacement circuit generator, and an auxiliary circuit insertion process for inserting the auxiliary circuit generated by the auxiliary circuit generator into the ladder diagram program, characterized by, the ladder diagram program creation assistance device is configured to determine if a step comprising a coil of a contact belonging to the partial circuit selected by the partial circuit selector appears in the ladder diagram program and, if the determination is positive: the program editor is configured to prohibit replacement of the partial circuit appearing after the step with the replacement circuit in the replacement process; or the program editor is configured to insert the auxiliary circuit generated by the auxiliary circuit generator between the step and a step in which the partial circuit first appears after the step in the auxiliary circuit insertion process. a partial circuit selector, configured to select a partial circuit comprising a plurality of contacts (a, b, c, A) in a ladder diagram program and appearing more than a predetermined number of times; a replacement circuit generator, configured to generate a replacement circuit comprising a smaller number of contacts (a, b, c, A) than the partial circuit selected by the partial circuit selector; an auxiliary circuit generator, configured to generate an auxiliary circuit that causes the replacement circuit generated by the replacement circuit generator to perform a same action as the partial circuit selected by the partial circuit selector; and a program editor, configured to perform, on the ladder diagram program, a replacement process for replacing a partial circuit appearing in the ladder diagram program with the replacement circuit generated by the replacement circuit generator, and an auxiliary circuit insertion process for inserting the auxiliary circuit generated by the auxiliary circuit generator into the ladder diagram program, characterized by, the ladder diagram program creation assistance device is configured to determine if a step comprising a coil of a contact belonging to the partial circuit selected by the partial circuit selector appears in the ladder diagram program and, if the determination is positive: the program editor is configured to prohibit replacement of the partial circuit appearing after the step with the replacement circuit in the replacement process; or the program editor is configured to insert the auxiliary circuit generated by the auxiliary circuit generator between the step and a step in which the partial circuit first appears after the step in the auxiliary circuit insertion process. the program editor is configured to prohibit replacement of the partial circuit appearing after the step with the replacement circuit in the replacement process; or the program editor is configured to insert the auxiliary circuit generated by the auxiliary circuit generator between the step and a step in which the partial circuit first appears after the step in the auxiliary circuit insertion process.