A wastewater treatment device for decomposing solid matter using aerobic microorganisms in a bacteria bed, includes a decomposition tank that accommodates the solid matter obtained by crushing food waste and the bacteria bed, a water supply capable of supplying water to the decomposition tank, and a stirrer for stirring the solid matter and the bacteria bed in the decomposition tank. The bacteria bed includes a carrier made of a synthetic resin having a plurality of pores and microorganisms carried in the plurality of the pores.