PURPOSE: To enable only a specified person to read a data memory to which an access is possible with execution of an instruction of an application program by using the memory as a specific address identification symbol data setting memory and permitting a command processing operation only when a specific identification symbol is set at the setting memory.

CONSTITUTION: A programmable controller consists of a CPU part 1 which performs the overall control of a PC system, an I/O part 2 which transfers the input/output information to various equipments, a system ROM 3 which stores a monitor program, an RAM 4 which stores an application program, and a RAM 5 which stores the accessable data memory. In such a constitution, an identification number setting memory is added to a data memory serving as an accessable area. Then a program is produced so that the setting memory can be cleared with execution of an instruction after the process related to the identification number is through. Thus it is possible to perform a normal reading action and also to change the identification symbol data.