To provide a stormwater separated catchment device capable of making the separation and elimination of fine-grains and, at the same time, having difficulty choking to raise collecting efficiency.

A down-pipe drained below is provided to a rain gutter of a building, a collecting pit 9 extended in the lateral direction is provided to the down-pipe and, at the same time, in the stormwater separated catchment device providing a water storage tank storing rain water W flowing down through the collecting pit 9 from the down-pipe, the collecting pit 9 is equipped with an inner cylinder 21 communicated with the down-pipe, at the same time, extended in the lateral direction and provided with a filter section 20, and an outer cylinder 22 covering the inner cylinder 21 and, at the same time, a cylindrical collecting space 25 formed between the inner cylinder 21 and the outer cylinder 22 and communicated with the water storage tank.