PURPOSE: To attain the debugging of a program even in language having no function of outputting information relating to debugging by forming the information relating to debugging not by a compiler but by a linker.

CONSTITUTION: The inlet name of a module to be debugged is inputted by an inlet name inputting means 9 and whether the inlet name is registered or not is checked by an inlet name segment input means 10. When the inlet name is registered as the inlet name of a module to be debugged, an inlet descriptor corresponding to the inlet name is extracted by an inlet descriptor segment input means 11 and control is transferred to an extracted branch instruction embedding means 13. The embedding means 13 inputs a corresponding procedure segment through a procedure segment input means 12. An instruction specified by the extracted inlet descriptor is saved to the expanded part of the inputted procedure segment and an instruction to be branched to a debugging module is embedded in the position of the instruction. Thus, the module to be debugged is executed.