A valuable-medium monitoring system of the present disclosure includes terminal devices and a server, the terminal devices each including a controller that extracts information on a valuable medium and determines whether or not the valuable medium is a circulation-unsuitable medium based on the extracted information on the valuable medium; and a transmitter that, in response to a determination that the valuable medium is a circulation-unsuitable medium, transmits information on the circulation-unsuitable medium to the server, the server including: a memory that stores pieces of information on circulation-unsuitable media, the pieces of information being grouped into groups; and a transmitter that, in response to transmission of information on a circulation-unsuitable medium from one of the terminal devices, transmits a specific group of information on a circulation-unsuitable medium to which the circulation-unsuitable medium corresponds to any other terminal devices satisfying a predetermined condition.