The invention discloses a detector for detecting metal dangerous materials, which comprises a DC power supply, a switch, a loudspeaker, a high-frequency transformer, a zener diode, a first diode, a second diode, a first potentiometer, a second potentiometer, a first triode to a fifth triode, a first capacitor to a seventh capacitor, and a first resistor to a fifteenth resistor. When the primary coil of the transformer approaches a metal object, eddy current is generated in the metal conductor, energy loss in an oscillating circuit is increased, positive feedback is weakened, oscillation of an oscillator in a critical state is weakened, the lowest energy needed for oscillation can not even be kept to enable oscillation of the oscillator to stop, the change is detected via the circuit, the change is converted into a sound signal, and according to existence of the sound, whether the metal object is below the coil can be judged and detected. The detector for detecting metal dangerous materials has the advantages that the structure is simple, adopted elements are few, the size is small, the cost is low, manufacturing is easy, sensitivity is extremely high, and small metal dangerous materials and covered metal dangerous materials can be easily detected.