PURPOSE: To control easily an external memory medium by securing such a mechanism where a program to be executed next is loaded automatically by setting again the external memory medium after a power-off mode in a specific state where the program under execution should be changed.

CONSTITUTION: When some fault occurs in a general transaction mode where a normal business program is executed by an ATM, it is decided whether the operator's processing is needed or not. When the processing of a customer engineer CE is needed, it is decided that a CE program must be loaded as long as the specific CE processing such as a test for cash reception/payment, etc. excluding a mode where the general CE processing is effective. Then the control proceeds to a rewriting program for iPL information in a step n10. Thus the iPL information within a floppy disk is rewritten. In a fault processing mode a floppy with which the iPL information is rewritten in the step n10 is set again to turn on a power supply. Thus a specific CE program is loaded. The iPL information is written again in a step n20 before execution of the specific CE program. Then the corresponding program is executed.