Rainwater collecting device for building roof

The invention relates to a rainwater collecting device, in particular to a building roof rainwater collecting device which is timely and convenient to clean and high in rainwater collecting efficiency. The device comprises a roof, a rainwater collecting groove is formed in the roof, a collecting box corresponding to the rainwater collecting groove is arranged on the side face of the roof, the roof further comprises a filtering net bag, a limiting frame, a fixed toothed plate, a lifting toothed plate and a gear, the filtering net bag is arranged in the collecting box and connected with the limiting frame, and two symmetrically-arranged first sliding blocks are arranged on the side face of the limiting frame, a first sliding groove is formed in the collecting box, springs are arranged on the bottom faces of first sliding blocks, a wheel shaft of a gear is fixedly installed on the collecting box, a fixed toothed plate is installed on the limiting frame and matched with the gear, a lifting toothed plate is movabl