1. A program conversion device comprising: a program storage unit operable to store therein an original program that includes a secret operation instruction to perform a secret operation using secret information on operand information; a split secret information generation unit operable to generate pieces of split secret information based on the secret information and a predetermined combining operation, such that the secret information is acquired by performing the combining operation on the pieces of the split secret information; a split secret operation instruction generation unit operable to generate, for each of the pieces of the split secret information, a split secret operation instruction to perform a split secret operation using the operand information and the piece of the split secret information; a combining instruction generation unit operable to generate a combining instruction to combine results of the split secret operation using the combining operation, such that a result that is the same as a result of the secret operation is acquired; and a replacement unit operable to replace the secret operation instruction included in the original program with the split secret operation instruction and the combining instruction.