Abstract: By executing an additional link process, unresolved external reference information of object modules of new-version subroutines is resolved based on external reference information which is resolved when load modules are created, and a reference table for storing entry points of old-version subroutines and new-version subroutines and an additional load module are created. When an additional load process is executed, the additional load module and reference table dynamically loaded into a memory and a machine instruction of the entry points of the old-version subroutines is rewritten as a trap instruction. If the load module including the old-version subroutines are being executed, the execution of the load modules is continued by calling a control continuation process. When the old-version subroutines are called after the new-version subroutines are loaded in the memory, the new-version subroutines are called by executing a control transfer process.