A utility knife has a housing, a blade support adapted to carry a blade and shiftable in the housing between a cutting position in which the blade projects from the housing and a safety position in which the blade is retracted into the housing, and a handle pivotal on the housing from a starting position in a first direction into an open position in which the blade in the support can be replaced and from the starting position in a second direction opposite the first direction into an active position operatively engaging the blade support and displacing same into the cutting position. An actuation element is movable on the housing between a first position blocking movement of the handle into the open position and a second position blocking movement of the support into the cutting position.