Abstract: The purpose of this invention is a long-blade cutter with adjustable blade extension and retractable blade guard including an elongated body in which the blade can retract, a slider capable of moving the blade in its plane, a blade holder/loader within which the blade can slide, characterized in that it also includes a safety guard made up of an extended element that can cover the edge of the blade over its full length, arranged movable between a fully retracted position inside the body and an extended position over the entire length of the blade at its position of maximum extension, an elastic recall link mechanism interposed between said safety guard and the slider, means of driving the guard by said slider and a push-button for disengaging said means of driving.