A safety device that can close the paper passage of a shredder has a touch board pivoted in the vicinity of the shredder opening. When the board is under a pressure produced by fingers touching the opening, it is rotated about its pivotal axis. Its rotation drives a transmission mechanism and a closing element to close the opening. Therefore, the fingers cannot go into the opening and get hurt. Once the pressure on the touch board disappears, a restoring element pushes the touch board back to its normal position and brings the closing element away from the closing position. The opening is thus open again.