The invention relates to a bending machine, in particular to an automatic die changing device of the bending machine. The automatic die changing device of the bending machine comprises a slide block, and a clamping device is arranged at the lower end of the slide block; the slide block is provided with at least two suits of chain drive devices in parallel, each chain drive device comprises chain wheels and an annular chain engaged to the chain wheels, the chain wheels are connected with a drive motor through a rotating shaft, the annular chain vertically winds the slide block, the annular chain is provided with a plurality of connecting components, the connecting components are hinged to a die handle, the slide block is provided with a lifting lead rail, the connecting components are in sliding connection with the lifting lead rail, and the lifting lead rail is connected with a longitudinal move device. The automatic die changing device of the bending machine has beneficial effects that the automatic degree is high, the die change efficiency is improved, and the labor intensity of the operators is lowered; the structure is reasonable, the service life is long, because the connecting components are hinged to the die handle, the die and die handle always locate at a vertical state under the gravity, and therefore, the space usage is small.