A quenching depth measuring method is used for measuring the quenching depth in a workpiece and includes the steps of: magnetizing the workpiece by disposing, in the vicinity of the workpiece, a magnetizer equipped with an exciting coil; detecting, through a detection coil, an induced magnetic field generated by the magnetization; measuring the induced magnetic field as the output voltage of the detection coil; and specifying the thickness of the quenched hardened layer of the workpiece on the basis of known electromagnetic characteristic information of an unquenched material and a fully-quenched material and an output voltage value measured by the detection coil, the unquenched material being made of the same material as the constituent material of the workpiece and being a material on which a quenching process is not performed, the fully-quenched material being a material on which the quenching process is performed.