The present invention relates to a shredder having a thickness triggering device. During the shredding operation, the trembling of the article is minimized or eliminated by using the shredder. The shredder includes a sustaining mechanism and a driving assembly. Since the sustaining mechanism is sustained against the shredding article, the amplitude of the trembling article is largely reduced. As a consequence, the influence of the shredding article on the thickness triggering device is reduced so as to prevent interruption of the shredder.