Abstract: A workpiece processing apparatus includes: a cabinet having a projection chamber, workpieces being subjected to processing in the projection chamber; a projector configured to project projection media toward the workpieces charged into the projection chamber; an image sensor configured to image the projection chamber to form an image; and a control unit configured to output information relating to presence or absence of a residue in the projection chamber based on an initial image and an inspection image, the initial image being an image formed by the image sensor and being an image of the projection chamber with no workpiece remaining, the inspection image being an image formed by the image sensor and being an image of the projection chamber after discharging processing in which the plurality of workpieces are discharged from the projection chamber.