An apparatus of detecting defects on an optical recording medium includes a defect signal generating circuit for generating a corresponding defect signal according to a surface defect of the optical recording medium, a first synchronous signal generator for generating a first synchronous signal, a defect signal locating circuit, a delay signal generating circuit, and an OR gate. The defect signal includes at least one pulse, whose width corresponds to the physical width of a surface defect. The delay signal generating circuit generates a delay signal corresponding to each pulse when the spacing between two adjacent pulses is smaller than a preset value. An OR operation is performed to the delay signal and the defect signal to obtain a defect extension signal. The first synchronous signal and a second synchronous signal for separating data recording sectors of the optical recording medium are employed to detect widths and addresses of surface defects.