A trawl net of which the codend has the two-level construction of two bags; the upper bag for target species and the lower bag for marine debris, was developed with the bycatch exclusion window (BEW) at the top panel of the upper-bag to reduce bycatch and labor force for on-deck sorting. Fishing experiments of this trawl net were carried out in a coastal trawl fishery in Choshi, Chiba Prefecture. The recovery ratio in weight of the upper bag for target species was over 90%, and that of lower bag for marine debris was about 50%. Thus, the two-level construction of the two bags separated target species from marine debris, and therefore was helpful for fisher's on-deck sorting. Probabilities of fish encountering the BEW and the mesh selection curves were also estimated for several species from the catch data of the experiments. The BEW reduced crimson seabream of body size smaller than marketable size with little loss of target species, southern rough shrimp, although both of the two species had body sizes of enough small to pass through the mesh of BEW. The separation performance of the BEW was attributed mainly to the difference between the two species in encounter probability depending on fish behavior in the codend, as well as the mesh selectivity.