A folding knife having a cantilevered leaf spring member with an engagement tab at the free end thereof. The engagement tab engages with a notch defined in a pivoting blade carrier pivotally connected to the knife handle member. Carried within the blade carrier is an interchangeable blade insert. When the blade is moved to an extended position, it is automatically locked in that position through engagement of the engagement tab with the notch in the blade carrier. Retraction of the blade requires pulling upwardly on ears provided adjacent the engagement tab to remove the engagement tab from the notch, such that the blade can be pivoted into a blade compartment provided in the handle member.