PROBLEM TO BE SOLVED: To enhance protection effects on an induction type power supply system.SOLUTION: A method used for an induction type power supply system, for detecting whether an intruding metal exists in a power transmission region of the induction type power supply system, includes the steps of: interrupting at least one driving signal of the induction type power supply system to stop driving a supplying side coil of the induction type power supply system; detecting an attenuation status of a coil signal on the supplying side coil when driving of the supplying side coil is interrupted; and determining whether the intruding metal exists in the power transmission region of the induction type power supply system according to the attenuation status of the coil signal.SELECTED DRAWING: Figure 2