PURPOSE: To eliminate the excess and deficiency of buffer materials by arranging a sensor for sensing the state of the buffer material on a material supplying system buffer part provided between the spring correcting unit and material supplying unit of a coil spring manufacturing device.

CONSTITUTION: The spring material 1 of a material supplying system buffer part 3 is positioned in an ordinary state at a reference position as shown by a solid line, but when the delivery of a material supplying machine 4 is quickened, a spring material 1 is detected by a sensor 6 to permit the delivery speed of a correcting machine 2 to be raised. Further, when the delivery of the correcting machine 2 is interrupted, the spring material 1 is detected by a sensor 8, permitting the material supplying machine 4 to be stopped. Further, in case the spring material 1 is broken, the lack of the spring material 1 is detected by the sensors 10 or 11, allowing the correcting machine 2 and the material supplying machine 4 to be urgently stopped.