Abstract: A cutter type knife having a handle with a blade disposed to slide axially within the handle. Elements are provided for manually deploying the blade and automatically retracting the blade when a manual operating element is released. The manual operating element is a member adapted to be at least partially retracted into the handle. An additional part is adapted to convert movement of the aforementioned member into axial movement of the blade within the handle. In this way, retracting the aforementioned member deploys the blade. Also provide is a latch or lever for initially impeding retraction of the aforementioned member, whereby an initially greater force is required in order to begin retracting the member and thus deploy the blade.