A utility knife for use with a replaceable flat blade, has an elongated housing having a longitudinally extending guide open at the front end, a longitudinally extending and transversely open slot, and a longitudinally extending holding face directed transversely opposite to the stop. A blade holder having a seat for the blade is slidable in the housing between a front use position forwardly bearing on a longitudinally displaceable stop and with the blade projecting longitudinally forwardly from the guide past the front end and a rear storage position with the blade wholly contained in the housing rearward of the front end and the holder out of engagement with the stop. The stop can be secured in any of a plurality of longitudinally offset positions in the housing to adjust the front position of the blade.