Replacement of a signal address referred to in a sequence program is carried out by storing in advance, before-after replacement information which specifies the relationship between signal addresses before replacement and signal addresses after replacement in a format with a specifying of range. Based on the stored before-after replacement information, all the signal addresses to be replaced are searched for in the editing target sequence program or replacement target symbol information. Replacement of a searched signal address with a corresponding after-replacement signal address is executed in accordance with the before-after replacement information.