Leakage preventing device of electromagnetic wave and wireless power transmission system

According to an embodiment, there is provided a leak preventing device of electromagnetic wave, including a metal pipe and a magnetic material part. The metal pipe is arranged to surround a periphery of a first electric power transmission device. The first electric power transmission device wirelessly transmits electric power to a second electric power transmission device via an electromagnetic wave. The second electric power transmission device is opposed to the first electric power transmission device. An opening is formed on the metal pipe along a circumferential direction of the metal pipe. The magnetic material part is arranged within the metal pipe along the circumferential direction the metal pipe.