A device and method can optically detect a defect of a round wire rod to be tested, and particularly, remotely detect the defect without contact in real-time. The device includes a lighting device for emitting circular surface light to the round wire rod; an optical sensor for generating an optical signal by receiving the light reflected from the round wire rod, which is being transported, and converting the optical signal into an image signal; and a signal-processing unit for acquiring surface information of the round wire rod by receiving the image signal from the optical sensor.