An error rate measuring apparatus includes error counting means for comparing bit string data obtained by converting a signal received from the device under test with error data, counting the number of FEC symbol errors by each codeword length in a case where the number of FEC symbol errors is less than the threshold value, and collectively counting the number of FEC symbol errors of codeword lengths in a case where the number of FEC symbol errors is equal to or greater than the threshold value, and display control means for displaying and controlling a list of collected results of the number of FEC symbol errors of each codeword length.