Abstract: A carton opener has a blade holder for receiving and holding a single edged razor blade. A sheath has a body portion including two side walls closely fitted about the blade holder in which the blade holder is capable of sliding within the sheath between a blade retracted position to at least one blade extended position. A slot is formed on one of the side walls longitudinally along the length of the sheath. A moving member is attached to the blade holder and extends from the blade holder through the slot and is in registry with the slot for moving the blade holder longitudinally with respect to the sheath. The moving member includes a detent biased to a side of the slot having recesses for releasably engaging the recesses when the detent is adjacent thereto.