A mine roof support frame has a pair of spaced-apart floor skids on which hydraulic props support a roof engaging structure. A shifting mechanism with a ram in a trough-like housing and a guide beam is positioned between the skids and serves to displace the frame relative to a scraper-chain conveyor and vice versa. The guide beam is a flat plate with a width more or less the same as the space between the skids and rests directly on the floor. The piston rod of the ram is coupled to the guide beam near the conveyor, the ram cylinder is coupled to the housing and the housing is coupled to the skids at the stowage end. The ram housing has a guide rail on the underside which mates with a guide element on the top of the guide beam. Levers pivotably coupled to the floor sills in front of the ram housing are operated by piston and cylinder units to engage on the guide beam to lift the floor skids partially during advancement of the frame.