Abstract: A folding knife that is assisted by a spring force in extending a blade thereof provides an effortless and safe structure of folding knife. The folding knife includes opposite handle plates and clamp plates that clamp a blade therebetween. The blade has a surface forming a raised portion that defines a cam ring having a caroming contour surrounding a pivot hole of the blade. The cam ring is received in a hollow opening formed by stamping one of the clamp plates to be engageable with a spring arm arranged in the opening. The camming contour and the resilience of the spring arm help realizing effortless and resiliency-assisted extension of the blade. The other clamp plate forms a slot that defines a resilient sideway-deflected positioning plate engageable and thus retaining the blade at an extended position. Advantages of effortless extension of blade and operation safety by the blade can be achieved.