To facilitate the positioning of the blade of a folding knife and a blade lock mechanism by pivotally supporting the blade of the folding knife by means of an eccentric pivot pin having two independent axial centers.

The folding knife 2 is provided with the blade 4 having a hole 34 for a pivotally supporting pin which is pivotally supported to a handle part with the eccentric pivot pin 10. The handle part is provided with a liner lock 20 and the liner lock 20 has a lock arm 22 to be engaged with the rear end 8 of the blade when the blade 4 is in an extending position. The eccentric pivot pin 10 is provided with a head 50, a lock spline 28 and a pivot pin rotary surface 48 to be locked with the blade hole 34 and is fixed by screwing with a fastening screw 12. Then, the center line 30 of the lock spline 28 is deviated from the center line 32 of the pin rotary surface 48 so that the blade 4 is positioned by the rotary operation of the eccentric pivot pin 10.