Disclosed is an auto-feed built-in a paper shredder, including a pair of bisecting lids that are each provided at an inside thereof with a paper press, a paper receiving compartment, an auto-feed, and a paper shredding device located exactly below the auto-feed, wherein the auto-feed includes a paper tray, a paper inlet and two roller assemblies; the paper inlet and the paper shredding device located therebelow are aligned along an identical central axis; the two roller assemblies are provided at opposing sides of the paper inlet in parallel and project into the paper tray, whereby after placing a pile of paper into the paper receiving compartment to be supported by the paper tray, and closing the bisecting lids, the paper presses provided at the insides of the lids would apply a force against the pile of paper, such that a bottommost paper of the pile of paper would be folded in half by the two rollers rotating towards each other and then fed into the paper inlet to be subsequently shredded by the paper shredding device located below the paper inlet.