A guide rail mechanism used for, for instance, a die boding apparatus and a wire bonding apparatus, including a pair of guide rail sections that face each other and convey a workpiece such as a lead frame in between. The guide rail sections include rail height adjustment spacers held by spring force between guide rails and guide rail stands, and this rail height adjustment spacer is replaced for other rail height adjustment spacers of different thicknesses by moving guide rail raising-and-lowering shafts by way of overcoming the spring forces of the springs provided thereon, thus assuring the same upper surface height level of workpieces of different thicknesses to be conveyed.