To prevent an increase in program size for memory access, in a multitask system having a memory access function by a register relative addressing mode.

A specific index value is prepared in each task as an index value used in an address calculation by relative addressing. That is, an index value '0x00008000' is made to be held with respect to a task A, and an index value '0x00014000' is made to be held with respect to a task B, respectively, as the context information of the tasks. When an OS changes over the task, the OS stores the index value corresponding to the task of a changeover destination in an index register. When generating a program (an execution file), a linker such that an address solution is performed by use of the given index value specific to each task is prepared, and linkage is performed. Thereby, each task can have a specific relative addressing space.