An autoretracting box-cutting knife has a housing dimensioned to be held in the hand and having a longitudinally forwardly projecting front end, a blade slide displaceable longitudinally in the housing between a front position and a rear position, and a blade secured in the slide, projecting forward from the housing in the front position of the slide, and retracted back into the housing in the rear position of the slide. In accordance with this invention a blade-actuating crank has an inner and an outer end and is mounted on a pivot on the housing that defines for the crank a transverse pivot axis. Interengaging formations on the crank and holder offset from the pivot can move the crank with the holder between a rear position with its outer end projecting laterally from the housing in the rear position of the holder and a front position in the front position of the holder. A spring engaged between the slide and the housing urges the holder and the crank into the respective rear positions so that when the outer end of the crank is pushed forward to push the crank into the front position the slide is pushed forward into its front position and the blade projects from the housing.