An error rate measuring apparatus includes: an operation unit that sets a codeword length, an FEC symbol length, and an FEC symbol error threshold; error counting unit for counting FEC symbol error and an uncorrectable codeword; a display unit that performs display by setting one zone of a display area as one FEC symbol length, matching a zone length of a horizontal axis of the display area with one codeword length, and performing line feed in codeword length units according to presence or absence of the FEC symbol error in FEC symbol length units based on a counting result; search unit for searching for the uncorrectable codeword starting from the cursor on the identification display; and display control unit for performing display control of the cursor at a position of a head error of the searched uncorrectable codeword.