In an foreign body detection apparatus, an optical signal detection unit irradiates a light spot onto a surface of an object to be inspected while scanning the surface by employing the light spot in a predetermined direction, and receives a reflected beam from the surface of the inspected object to generate a photodetection signal corresponding to the light intensity of the reflected beam. A foreign body detection unit generates a foreign body detection signal appearing with respect to a leader and a trailer in the scanning direction of a foreign body adhering to the inspected object from the photodetection signal. The foreign body detection signal is obtained, for example, as a difference signal between the photodetection signal and a delayed photodetection signal with a predetermined delay time. A foreign body discrimination unit generates a foreign body discriminating signal indicating a region in which the foreign body is present from the foreign body detection signal.