PURPOSE: To normally answer an inquiry about commodity information even if a master device for backup is not regularly provided and even if a master device is unable to operate.

CONSTITUTION: Each slave ECR 3 has a PLU slave file 4 which stores and holds commodity information in a PLU master file 2 sent dispersedly to the slave ECR 3 from a master ECR 1 at specific timing. Further, once each slave ECR 3 detects the master ECR 1 being unable to operate, the inquiry about commodity information is simultaneously reported to the respective ECRs 3 in a similar manner. The slave ECR 3 having received the inquiry retrieves its PLU slave file 4 on the basis of the inquiry and answers corresponding commodity information to the inquiry source.