The utility model provides metal detecting device applied in a production line, which comprises detecting dot matrixes formed by at least one basic metal detecting unit and a control processing circuit, wherein the basic metal detecting unit comprises coil sensors and sensor drive processing circuits; each sensor drive circuit comprises an AC (Alternating Current) signal generating circuit, a coil impedance detecting circuit and a detection result processing circuit; AC signals generated by the AC signal generating circuits are sent to the coil sensors through the coil impedance detecting circuits; the equivalent impedances of the coil sensors are detected by the coil impedance detecting circuits simultaneously; when obvious csuspendes of the equivalent impedances are detected, metal materials are detected; the detecting signals are sent to the detection result processing circuits and processed into digital logic signals; the digital logic signals are output to the control processing circuits and the alarm output is carried out. In practical use, the amount of the basic metal detecting units can be increased or decreased according to the area to be detected.