A mechanical bin-full device for a paper shredder with a pressing plate, a contact switch, and a touching part. The pressing plate is installed at an outside portion of the shredder mechanical parts under the lower housing. One end of the pressing plate is pivots on the lower housing and the other end is free. The contact switch is fixed on the lower housing and a contact point is provided on the contact switch. The touching part is provided on the pressing plate, away from the mechanical parts. The lower housing has a through-hole under the contact point of the contact switch enabling the touching part to contact the contact point. The waste paper drives the pressing plate to turn around the joint between it and the lower housing, making the touching part touch the contact point of the contact switch and making the shredder power off.