Disclosed is a rainwater collecting apparatus capable of automatically discarding pollutant initial rainwater. The rainwater collecting apparatus structurally comprises a rainwater storage box, a dredging port, a drainer, an overflow water inlet pipe, an overflow water outlet, a drain pipe, an overflow collecting nozzle, a building down pipe, a filter screen and an automatic control hopper for pollutant initial rainwater. Roofing initial rainwater flows down from the building top surface through the building down pipe, and then flows down through the automatic control hopper for pollutant initial rainwater; with increasing of rainwater, only a part of the rainwater flows through the automatic control hopper for pollutant initial rainwater, water level rises continuously until reaching the overflow collecting nozzle, rainwater enters the rainwater storage box through the overflow inlet pipe, water level in the rainwater storage box rises continuously until reaching the overflow water outlet, so that rainwater flows over the overflow outlet and flows through the overflow water outlet and the drain pipe to enter the building down pipe. The rainwater collecting apparatus has the advantages of simple structure, convenience in processing, small size, low manufacturing cost, and capability of utilizing rainwater resource completely and improving quality of rainwater.