PURPOSE: To improve debugging processing efficiency by defining symbol information for each task as a module with one task and one load and enabling the mouse input of a debugging command as well in the case of debugging a multitask program, which is applied to a target such as a microprocessor system or the like, at a source level.

CONSTITUTION: A terminal 2 is connected through a communication line to a target 1, enables the input of the debugging command by a mouse 5 in addition to a keyboard 4 and executes the output display of the debugged result to a display device 3. In this case, one-task-one-load module constitution is provided, the symbol information is loaded and stored for the unit of a task, and source information is managed for the unit of the task as well. A main storage device 7 stores a symbol management table, an auxiliary storage device 6 is equipped with the load module having the source of a debugged system and the symbol information, the load module is loaded to the main storage device 7 as needed, and required information is read out to the debug while receiving the control of the terminal 2 receiving the input from the keyboard 4 and the mouse 5.