To accurately acquire an objective criterion for judging the capacity of data input operation by counting the frequency of data inputs inputted by a data input means and storing the count value correspondingly also to an operator.
The commodity sales data processor is formed by an electronic cash register 10, which is provided with a counting means (a CPU 11 and a ROM 12), a rotary table (number-of-items table 13I and a key frequency table 13N) and a count value storage control means (the CPU 11 AND THE ROM 12) so as to grasp the frequency of data inputs within a fixed time in each operator. The depression frequency of a clear key 20C which is generated during data inputting work is counted by a clear counting means (the CPU 11 and the ROM 12), a clear rotation table 13CN and a clear count value storage control means (the CPU 11 and the ROM 12).