A program development support system includes a reader, a designator, and a comparator. The reader is configured to read first and second programs executing operations which are expected to be identical to each other. The designator is configured to designate a variant pair of a first variant included in the first program and a second variant included in the second program. The first and second variants are expected to be identical to each other. The comparator is configured to compare values between the first and second variants when the first and second programs are executed.