To accurately diagnose a set examination reference value by diagnosing the examination reference value set after a prescribed number of times of use based on the examination reference value set in the prescribed number of times of use of a reference coin and on the cumulative number of times of use.

Data representing a feature amount of a reference coin provided by an examination sensor are transferred to a personal computer(PC), which calculates a mean value and a standard deviation of the feature amount as examination reference data. The PC also calculates an upper limit value LmtH1 and a lower limit value LmtL1 of a threshold for examination reference diagnosis by substituting examination reference data Ref1 set at the time of first use of the reference coin and a set number (n) of times of the examination reference data into a prescribed function equation. When examination reference data Ref(n) set after the second time are within the range of the upper limit value LmtH1 and the lower limit value LmtL1, these examination reference data Ref(n) are discriminated normal.