A banknote monitoring system, comprising: a plurality of banknote processing apparatuses (2a-2n); and a banknote monitoring apparatus connected to the plurality of banknote processing apparatuses (2a-2n) via a network, wherein the banknote monitoring system further comprises a terminal device and the plurality of banknote processing apparatuses (2a-2n) process a banknote with a serial number and transmit information including an average identification rate of the serial number to the banknote monitoring apparatus via the network, wherein the average identification rate of the serial number is a rate of the number of digits of the serial number read by the banknote processing apparatus (2a-2n) to the number of digits of the serial number, and the banknote monitoring apparatus is configured to: receive the information from each of the plurality of banknote processing apparatuses (2a-2n); calculate a monthly average identification rate of the banknote processing apparatus (2a-2n) as a whole per predetermined period; determine that a specification of the banknote has been changed when an absolute value of a variation determined from the average identification rate per predetermined period is greater than a first threshold; and transmit a specification change notification to the terminal device when the banknote monitoring apparatus determines that the specification of the banknote has been changed. a plurality of banknote processing apparatuses (2a-2n); and a banknote monitoring apparatus connected to the plurality of banknote processing apparatuses (2a-2n) via a network, wherein the banknote monitoring system further comprises a terminal device and the plurality of banknote processing apparatuses (2a-2n) process a banknote with a serial number and transmit information including an average identification rate of the serial number to the banknote monitoring apparatus via the network, wherein the average identification rate of the serial number is a rate of the number of digits of the serial number read by the banknote processing apparatus (2a-2n) to the number of digits of the serial number, and the banknote monitoring apparatus is configured to: receive the information from each of the plurality of banknote processing apparatuses (2a-2n); calculate a monthly average identification rate of the banknote processing apparatus (2a-2n) as a whole per predetermined period; determine that a specification of the banknote has been changed when an absolute value of a variation determined from the average identification rate per predetermined period is greater than a first threshold; and transmit a specification change notification to the terminal device when the banknote monitoring apparatus determines that the specification of the banknote has been changed. receive the information from each of the plurality of banknote processing apparatuses (2a-2n); calculate a monthly average identification rate of the banknote processing apparatus (2a-2n) as a whole per predetermined period; determine that a specification of the banknote has been changed when an absolute value of a variation determined from the average identification rate per predetermined period is greater than a first threshold; and transmit a specification change notification to the terminal device when the banknote monitoring apparatus determines that the specification of the banknote has been changed.