To provide an expansion drive mechanism which can be downsized even when a length of expansion is increases by eliminating necessity for providing a utility supplier of compressor or the like supplying compressed air.

This expansion drive mechanism 10, comprising a pinion 14 turned by a drive means and a rack 16 meshing with the pinion 14 to connect a mover provided movably in a prescribed direction to one end, moves the mover in a prescribed direction by turning the pinion 14 to extend/contract a protruding length protruded from the pinion 14 in one end side of the rack 16. The expansion drive mechanism 10 is characterized by providing a guide roller 20, provided turnably along an external periphery of the pinion 14, pressing the rack 16 to the pinion 14 to turn so as to hold their meshing conditions, when a meshing position between the pinion 14 and the rack 16 is changed by changing a tilt angle of the rack 16 according to movement of the mover in the case of its movement in a prescribed direction by extending/contracting the protruding length in one end side of the rack 16, and a support member 22 supporting the guide roller 20 to turn in its turn direction.