An apparatus for detecting a pallet full load state determines a pallet full load state while switching the upper limit value of the mounting height of workpieces according to workpiece size. The cell controller of an apparatus for controlling a sheet metal machining line estimates an occurrence or non-occurrence of a pallet full load state defined as a function of the overall height or the total weight of the workpieces loaded on the carrier pallet by analyzing the machining schedule when a machined workpiece is loaded on the carrier pallet and has a replacing carrier pallet good for the next workpiece to be loaded stand-by whenever appropriate. A workpiece identifying apparatus determines the XY dimensions of a batch of workpieces on a pallet by arranging a number of absolute reference points arranged on the pallet and a number of relative reference points arranged on the workpieces and calculating the differentials between the absolute reference points and the corresponding relative reference points and the XY dimensions of a square defined on the pallet. The workpiece identifying apparatus additionally determines the material of the workpieces from the surface images of the workpieces taken by the cameras it carries by sequentially referring to the surface image data stored in a surface image data storage master. The workpiece identifying apparatus further determines the thickness of each of the workpieces and the number of workpieces on the pallet by determining the height of the accumulated workpieces and the gaps between any adjacently arranged workpieces.