To determine to give notice that the measurement accuracy of an axle load measuring instrument is beyond permissible limits or lowered without running a test vehicle whose axle load is known. This axle load measuring instrument 1 measures the number of axles of a running vehicle 3, its wheel base, its axle load on each axle, and its total weight. The number of axles of a specific vehicle, the upper and lower limit values of its wheel base, and the lower limit value of front axle load, are previously stored in a storage part 23. These data are compared with measurement values such as the wheelbase of the running vehicle 3 to determine whether the running vehicle 3 falls under the specific vehicle. If the running vehicle 3 falls under the specific vehicle, the moving average value of total-weight measurement values is compared with the total-weight upper and lower limit values of the specific vehicle stored in the storage part 23. If the average value does not fall within a range defined by the upper and lower limit values, an arithmetic and control part 20 transmits, from a communication part 25 to a higher-rank device 8, a message to the effect that the weight measurement values of the specific vehicle stands outside an allowable range.