According to one embodiment, an electromagnetic wave attenuator includes a multilayer member, and a magnetic member. The multilayer member includes a plurality of magnetic layers and a plurality of nonmagnetic layers. The plurality of nonmagnetic layers is conductive. A direction from one of the plurality of magnetic layers toward an other one of the plurality of magnetic layers is aligned with a first direction from the multilayer member toward the magnetic member. One of the plurality of nonmagnetic layers is between the one of the plurality of magnetic layers and the other one of the plurality of magnetic layers. A thickness along the first direction of the magnetic member is not less than ½ of a thickness along the first direction of the multilayer member.