A paper shredder includes a chassis on which an automatic paper feeding opening is defined, a paper shredding mechanism, a paper separating mechanism located adjacent to the automatic paper feeding opening, and a paper pickup mechanism located between the paper separating mechanism and paper shredding mechanism. The paper separating mechanism includes a first paper supporting board on which a fastening mechanism is provided and a paper separating board cooperating with the fastening mechanism. The paper pickup mechanism includes a holding bracket, a paper pickup roller axe, a plurality of paper pickup rollers sleeved on the axe, a second paper supporting board located below the plurality of rollers and secured onto the second paper supporting board, and a third paper supporting board located above a distal end of the second paper supporting board and connected with the paper separating mechanism.