To easily reuse a data conversion design definition, which is not reused conventionally in the data conversion design definition.

This data conversion design unit or the like has a conversion source file definition information acquiring part 31 and a converted file definition information acquiring part 32 for acquiring data structure of a conversion source data 51 to be converted, and data structure of a converted data when it is converted, a conversion source/destination item correspondence defining part 13 and a conversion source/destination item conversion defining part 14 for reading out data conversion definition information already defined, from a storage device 4, and a data conversion definition generating part 15 for generating data conversion definition information for converting the conversion source data to be converted, to be stored in the storage device 4.