1. An apparatus comprising a memory; and a processor coupled to the memory and configured to: duplicate a process code of a variadic template function that has a variable number of parameters included in a source code, in association with each of actual arguments included in an actual-argument list corresponding to a variadic parameter defined by a variadic operator that packs the variable number of parameters of the variadic template function; perform a substitution process including substituting, in each of the duplicated process codes, another parameter that is one of parameters of the variadic template function and different from the variadic parameter, with a prepared parameter that is prepared to accept an actual argument, in the actual-argument list, that is associated with the each duplicated process code; in a case where the another parameter in each process code becomes an actual argument of another function different from the variadic template function, execute a search process of searching for a first function which matches a type of the another parameter or a generation process of generating the first function, based on a template function included in the source code, and substitute a first code for calling the another function with a second code for calling the first function which is acquired through the search process or the generation process; and perform a function parameter-pack expansion process including: firstly inserting, into a recursive call part in a process code of the variadic template function, a first one of the duplicated process codes that is associated with an actual argument at a head of the actual-argument list, and repeating an insertion process of inserting, into a recursive call part in a previously inserted one of the duplicated process codes, a next one of the duplicated process codes associated with an actual argument that is subsequent, in the actual-argument list, to an actual argument associated with the previously inserted one of the duplicated codes.