A surface flaw detector includes a light source capable of generating a laser beam, a material conveyance means provided for conveying a material to be examined in the direction transverse to the axis of the material and designed to let the material rotate on its axis at a fixed position or along the direction of conveyance, means for scanning the laser beam on the surface and in the axial direction of the material which is rotating on its own axis, optical means adapted to transmit the light reflected from the surface of the material to form a stationary optic image of the scanning means, light receiving means provided at the image forming position, and processing means adapted to discriminate the flaw signal upon receiving the output from the light receiving means.