PURPOSE: A rainwater treatment device is provided to efficiently remove contaminants and soil from rainwater even if a large amount of rainwater flows in a short time. CONSTITUTION: A rainwater treatment device(10) comprises a main body(300) and a bypass channel(400). Rainwater flows into the main body through an inlet(110) and an opening and closing unit(120). The main body filters the rainwater. When the opening and closing unit is closed, the bypass channel directly discharges the rainwater to the outside through an outlet(210). The bypass channel has one or more flow velocity reducing units(410). The flow velocity reducing units reduce the flow velocity of the rainwater flowing through the inlet.
