The DC magnetization is one of the common causes of operational faults in forward DC-DC converters because it may promote magnetic saturation in the transformers. A useful remedy is to detect the DC magnetization using a sensor and eliminate it by a controller. The purpose of this paper is to propose a simple but reliable sensor. Although a number of sensors have been proposed in prior works, they often suffer from complicated implementation or from influence of the load current on the sensor output. The proposed method, on the other hand, can be implemented only by a search coil equipped on the power transformer without adding any special physical structure except a through-hole on the core. Despite of the simple implementation, the method is not affected by the load current and can detect the DC magnetization before apparent magnetic saturation occurs. This paper also presents an experiment, which verified that the load current does not affect the sensor output and that the DC magnetization can be detected even under the flux density below the saturation level. These results support usefulness of the proposed sensor in practical applications.