To provide a metal detecting device capable of reducing cost, and capable of miniaturizing the device, by constituting a power circuit of the small number of paper items.

This metal detecting device 1 has a detecting circuit 6 for undamagingly detecting a metal body 4 embedded when boring a hole in a wall 3, a floor and the ground surface by using an electric drill 2 using a commercial power supply 8 as a power supply, and the power is supplied to the detecting circuit 6 by the power circuit 7 formed by connecting a rectifying diode 12 and a constant voltage diode 13 in inverse series to each other, between secondary side terminals of a voltage reducing transformer 9 for reducing a commercial source voltage.