This program development device comprises: a storage unit which holds a project; and an update means which imports one or a plurality of program modules into the project. Each of the program modules contains a program, and can define a first variable which is a variable that can be referenced among all program modules, a second variable which is a variable that can be referenced among the plurality of program modules, and a third variable which is a variable referenced in each program module. The update means maintains the variable name of the first variable contained in the imported program module, and when the variable name of the second variable contained in the imported program module overlaps the variable name of the second variable contained in any of the program modules of the project, the update means accepts a change of the overlapping variable name.