A source program memory section stores message groups classified as first to fourth message groups according to languages or operator skill levels, together with ladder data, symbolic data, and other types of data of a sequence program. A message group is selected and its data is stored in a first memory section. The message group data in the first memory section is read into an editing memory section and edited; the edited message group data is stored in a second memory section. The data stored in the first or second memory section is sent to a programmable controller in a numerical controller.