An error rate measuring apparatus includes: an operation unit that sets a codeword length, an FEC symbol length, and an FEC symbol error threshold in accordance with a communication standard of a device under test W; error counting means for counting FEC symbol error detected at one FEC symbol interval and an uncorrectable codeword; a display unit that identifies and displays bit string data according to presence or absence of the FEC symbol error in FEC symbol length units based on a counting result; and display control means for performing display control by setting one zone of a display area of identification display 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.