An air bed conveying system conveys a workpiece while the workpiece is being floated by air under pressure which is ejected from a plurality of air ejection holes defined in air bed blocks that are supported on respective support blocks. Each of the support blocks is of an integral box-shaped configuration and made of a quartz material having a low thermal expansion coefficient. A plurality of vertical position adjusting mechanisms are disposed underneath each of the support blocks, for adjusting the support block in vertical position.