The present invention relates to an automatic shredder without choosing the number of paper to be shredded which comprises a shredder core and an automatic paper feeding device, the automatic paper feeding device comprises a driving mechanism, a paper support box, a pick-up mechanism and a paper press box, the driving mechanism is fixed on the shredder core and connected with the pick-up mechanism for driving the pick-up mechanism, the paper support box comprises a first zone and a second zone, the pick-up mechanism is positioned between the first zone and the second zone and fixed to the paper support box, and its paper feeding direction is towards the second zone, one end of the paper press box is pivoted with the paper support box, the other end of the paper press box is connected detachable with the paper support box, the paper support box is fixed on the shredder core, and the second zone has a paper inlet positioned above the blade assembly of the shredder core, a magnet is positioned in the first zone, the automatic shredder further comprises an elastic paper press and retaining device mounted inside the paper press box and extending to the first zone, the magnet corresponds to the elastic paper press and retaining device, so the present invention can deal with a very large amount of paper to be shredded at one time, has a simple and convenient operation, is designed dexterously, and has a concise structure and a economical cost.