To provide an apparatus for separating unnecessary parts of a field crop, with which operation for separating the unnecessary parts of the field crop in a remaining state of necessary parts is accurately and surely carried out, labor for operation is saved and efficiency is increased.

The stem part Ab and leaf parts Ac of a Welsh onion A being transported by a carrier conveyor 2 are picturized by the imaging camera 19 of an unnecessary part detection apparatus 18 and the separation starting position Ad of the unnecessary leaf parts Ac and epidermis Ae is determined by a determination controller 22 based on the image information. The separation unit 28 of an unnecessary part separation apparatus 25 is moved to a position approximately facing the separation starting position Ad of the Welsh onion A based on the determination controller 22, air G discharged from a pair of right and left air discharge parts 37 is blown on the separation starting position Ad of the Welsh onion A, the unnecessary leaf parts Ac and epidermis Ae are separated in a remaining state of the necessary leaf parts Ac.