A radio wave absorber according to an embodiment includes a plurality of metal particles including at least one kind of magnetic metal element selected from a first group of Fe, Co, and Ni. Each of the plurality of metal particles has a linear expansion coefficient of 1×10−6/K or more and 10×10−6/K or less. The radio wave absorber also includes a binding layer binding the metal particles and having higher resistance than the metal particle, wherein a volume filling ratio of the metal particles in the radio wave absorber is 10% or more and 50% or less.