PURPOSE: To obtain a measuring method of high precision and reliability for a surface defect even if there is irradiation unevenness in light in an optical fiber.

CONSTITUTION: A standard face state is measured by irradiating light on a master gage, stored as a reference value (S6), a stored reference value is reversed, a reversed value is formed (S9), a face state of a measuring object is measured by irradiating light on the measuring object, a measured value is stored (S8), an operation value adding the measured value and said reversed value is found (S10), and a defect of the surface of goods is detected by comparing the operation value with a preset threshold value (S11). Irradiation unevenness of light of an optical fiber is eliminated, exact defect inspection can be performed, maintenance can be performed efficiently and surely, performance is improved and a defect detection method of high precision is obtained.