This invention implements reduction in the amount of background-scattered light from a semiconductor wafer surface and highly sensitive inspection, without increasing the number of detectors. A surface inspection apparatus that detects defects on the surface of an object (semiconductor wafer surface) to be inspected, by irradiating the surface of the object with a beam of light such as laser light and detecting the light reflected or scattered from the surface; wherein a widely apertured lens with an optical Fourier transform function is disposed between the object to be inspected and a detector, a filter variable in position as well in aperture diameter is provided on a Fourier transform plane, and background-scattered light from the semiconductor wafer surface is effectively blocked, whereby only a signal from a defect such as a foreign substance is detected.