The present invention relates to an apparatus 1 that processes a surface of a substrate 9 to be processed. A processing module 3 is disposed so as to oppose the substrate 9. The processing module 3 is relatively moved with respect to the substrate 9 in a direction of movement parallel to a plane PL. A foreign matter on the surface of the substrate 9 or a raised portion of the surface is detected by the detection mechanism 10. A roller 12, preferably having a circular cylindrical configuration, of the detection mechanism 10 is disposed in the processing module 3. A rotation axis 12a of the roller 12 is parallel to the plane PL and intersects the direction of movement. The roller 12 is supported by a supporter 13 such that the roller 12 can be rotated about the rotation axis 12a. The rotation axis 12a is adapted to be displaceable in a direction intersecting the plane PL. Rotation of the roller 12 is detected by a rotation sensor 21.