A screwdriver for driving collated screws including a slide body coupled to a housing for reciprocal displacement in a cycle including a retraction stroke and an extension stroke. A lever pivotably mounted to the slide body carries at one end a cam pin received in a cam slot in the housing with the other end of the lever advancing successive screws in the screwstrip, the cam slot having first and second camming surfaces for selective engagement by the cam pin to vary the relative positionning of the lever to be different for the same position if the slide body in the housing in the retraction strokes than in the extension stroke.