Radio wave absorber

A radio wave absorber comprising:

• a resistive layer having a first main surface and having a plurality of first openings formed at equal intervals in a first direction along the first main surface;
• an electroconductive layer having a second main surface and having a plurality of second openings formed at equal intervals in a second direction along the second main surface;
• and
• a dielectric layer disposed between the resistive layer and the electroconductive layer in a thickness direction of the resistive layer, wherein
• a value obtained by dividing a larger value out of a first ratio and a second ratio by a smaller value out of the first ratio and the second ratio is 1.3 or more, the first ratio being a ratio of a size of the first opening in the first direction to a distance between the nearest first openings, and the second ratio being a ratio of a size of the second opening in the second direction to a distance between the nearest second openings.