A foreign matter removal method that removes foreign matter attached to a surface of a substrate having been subjected to predetermined processing. An edge of a rotating substrate mounted on a mounting stage is irradiated with misalignment measurement laser light. The misalignment measurement laser light other than the laser light blocked by the edge of the substrate is received, and power thereof is detected. The amount of misalignment of the substrate is calculated based on the detected power of the misalignment measurement laser light and a detected rotation angle of the rotating substrate. The misalignment of the substrate is corrected for based on the calculated amount of misalignment. After that, foreign matter removal laser light is irradiated, and a process gas that is to react with the foreign matter is jetted to the edge of the substrate. Consequently, the foreign matter attached to the substrate is decomposed and removed.