Abstract: A box knife has a handle and a blade that is carried in the handle such that a segment of the blade projects beyond one end of the handle. In addition, the handle has two guards which are hinged to it remote from the cutting edge of the blade, and these guards are capable of moving between an extended position and retracted positions, yet are spring biased to the extended position so they assume that position when the knife is not in use. When in the extended position, the guards lie to the sides of the blade to shield it and the cutting edge on it, but when the guards are in their retracted position the blade is exposed. Moreover, the guards have curved leading and lower edges so that when the knife is brought against sheet material that is to be slit, the guards merely roll along that surface of that material and allow the blade to penetrate the material.