PURPOSE: To prevent an error in writing from a remote monitoring device by storing important data on elevator safety in a first storage area, and forbidding writing in the first storage area.

CONSTITUTION: Since 8000 H is outputted in an address bus 12a, the most significant address line A15(12b) is H, so that one input of a NAND gate 29 is H. Since a switch 27 is open, the other input of the NAND gate 29 via a pull-up resistance 28 is also H, that is, the output of the gate 29 is L. Accordingly, one input of an AND gate is L so that an output of the AND gate 30, i.e., an output signal 26 for control of writing in a data memory 13c is L, irrespective of the state of a write control signal 24 from CPU 11. Therefore, even when a command to write FFH at address 8000 H is executed, the contents of the data memory part 13c remain 00H without change.