There has been disclosed in a Japanese Patent Publication No. 57-44128 an item counting system wherein a known number of items is first weighed to obtain a provisional average weight per item and, after any unknown number of items is added, the total weight is measured and then divided by the provisional average weight. The quotient of the division is rounded to the nearest integer to give the total number of items including the number of the added items. The total number thus obtained is used also to revise and increase the accuracy of the provisional average weight given previously. The total weight is divided by the total number to give a revised provisional average weight per item. This system, however, has a disadvantage that, if the number of the added items is too many, the quotient derived from the total weight divided by the provisional average weight may include an error which amounts to nearly an integer, resulting in giving an error of unity or larger to the total number obtained. In such a case any "rounding" operation on the quotient becomes nonsense as well as an investigation of the accuracy of the provisional average weight. Therefore, once an error is introduced in the total number, any of the thereafter following average-revising processes can not eliminate the counting error.