Invoice Amount Calculation Method, Invoice amount Calculation Device, and Printer Invoicing System

A manufacturer server 110 that calculates an invoice amount for an inkjet printer has a billing status acquisition unit 342 that acquires billing status information including actual print volume PV, which is the amount of ink used for actual printing not including maintenance during a specific period L1; an actual print volume calculation unit 343 that determines if actual print volume PV is less than or equal to a specific volume V1; and an invoice amount calculation unit 344 that calculates an invoice amount. When actual print volume PV is less than or equal to the specific volume V1, a first invoice amount, which is a fixed amount, is calculated as the invoice amount, and when actual print volume PV exceeds the specific volume V1, a second invoice amount is calculated based on the actual print volume PV as the invoice amount.