PURPOSE: To prepare account receivable information and account payable information by a processing system only by inputting returned goods information from a warehouse section.

CONSTITUTION: Sales information having a customer code, commodity codes, the numbers of units, unit prices is formed (step 102) by referring to a customer master file (c) and a commodity master file (d) in addition to returned goods information having a customer code, commodity codes and the numbers of units inputted from the warehouse section. On the other hand, account payable information having vendor code, commodity codes, the numbers of units, and buying first costs is formed by referring to a commodity master file (d) and a vendor master file (e) in addition to the returned goods information and then the number of returned goods is added (steps 103, 104) to the number of stored returned goods recorded in the commodity master file (d). Respective lists formed by allocating slip numbers to the prepared sales information and account payable information are outputted and checked (steps 107, 108) by an account receivable section and an account payable section and then the slip numbers are inputted, so that the data of internal credit and account payable data are displayed on a screen and necessary correction and data determination are executed (steps 109, 110).