An instruction drop-off warning system (1), which warns of drop-off of an instruction sheet (L) attached on a work (20) in a production line (40), comprises an IC tag (5a), which is incorporated in the instruction sheet L and is used for storing identification information, an instruction-management system (2), which manages the identification information of the instruction sheet (L) attached on the work (10) as instruction information (4), and a handy terminal (6), which includes a reader/writer (3) for reading and writing identification information from and into an IC tag (5b) and which stores the instruction information (4) received from the instruction-management system (2). In the instruction drop-off warning system, the handy terminal (6) is used for comparing the identification information being read from the instruction sheet (L) attached on the work (20), with the instruction information (4), so that a detection is made for warning whether or not any instruction sheet (L) has dropped off.