Disclosed is a folding knife with safety device, which includes a main knife, a revolving shaft, a first liner plate, a first rivet, a switch lock sheet, a first handle part, a second handle part, a second liner plate and a spacer sleeve. The first liner plate is provided with a resilient lock sheet, an elongated slot, a stopper portion, a first rivet, a second rivet and a third rivet; the switch lock sheet is provided with a first rivet slot, a skidproof rack, a second rivet slot, a labor-saving slot, a locking contact, and a buckle; and the first handle part is provided with an axle hole, a holding slot, a holding hole and a screw hole. The present invention has advantages of simple structure, easy of use and stable performance.