To provide a method and device for detecting buried metal, whereby it is possible to radio (wirelessly) transmit a synchronizing signal, and, when the frequency band of the transmission signal is restricted, to problem synchronous detection using a reference signal having a frequency equal to or greater than the frequency band. A method for detecting buried metal using synchronous detection method having a transmitting side device that transmits a transmitting signal (alternating current) to a buried metal for detection and transmits a synchronizing signal for synchronous detection, and a receiving side device for measuring the position and burial depth of the buried metal by detecting a magnetic field generated by the transmitting signal flowing in the buried metal with a magnetic sensor and processing amplitude and phase of the magnetic field, the method including: generating a standard signal of frequency f in the transmitting side device, and n dividing this standard signal to convert it to a transmitting signal of frequency f/n, transmitting this transmitting signal to the buried metal, m dividing the standard signal to convert it to a synchronizing signal of frequency f/m, transmitting this synchronizing signal from the transmitting side device by radio. Receiving the synchronizing signal by the receiving side device, m multiplying this received synchronizing signal to convert it to the standard signal. N dividing this converted standard signal to convert it to a reference signal of frequency f/n. Detecting a magnetic field generated by the transmitting signal flowing in the buried metal and synchronously detecting with the reference signal.