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 greater than, less than or equal to a specific volume V1; and an invoice amount calculation unit 344 that determines an invoice amount. When actual print volume PV is greater than the specific volume V1, the invoice amount is determined based on the actual print volume PV.