To provide a single-wafer basis washing device for a semiconductor substrate which can reduce washing process time by finishing washing process by observing the removal state of a surface oxide film without depending on washing time.

The device has a casing 2; a rotary table 4 which is provided to the casing 2, and rotated and driven by a driving shaft 3 and whereon a semiconductor substrate W is mounted and fixed; a washing solution supply nozzle 5 which is provided to supply washing solution to the surface of the semiconductor substrate W; and an oxide film detection sensor 6 which detects the removal state of an oxide film of a surface of the semiconductor substrate W and is provided to optically face the surface of the semiconductor substrate.