To obtain an auxiliary safe mechanism by which a folding knife blade is not accidentally closed from an extending position to a closing position by providing a thin and long slot which is substantially locked in the first extending position where the knife blade is positioned after extension from a handle at a first lock position.

When a safety latch 22 is at a release position, the stud 20 of the knife blade 8 is moved in a circular-arc shape by a seam plate hole 34 during rotation between the first extending position extended from the knife blade 8 and the second closing position. A seam plate 32 is positioned in the neighborhood of the base end part 12 of the knife blade 8 and the seam plate 34 receives the stud 20 so as to permit the rotation of the knife blade 8 with a pin as a center. When a safety lock arm 24 is in a front part position, it is positioned just above the stud 20. At this position, the point 10 of the knife blade 8 directed to the cavity of the handle is substantially prevented from being rotated downward.