To enable guide of sheets in a little fluttering manner.

A sheet guide face 4.7 has air passage opening portions 4.8, 4.8' parts of which serve as blow-out opening portions 4.8 for blowing an air into an air cushion and the remaining of which serve as flow-out opening portions 4.8'. The blow-out opening portions 4.8 and the flow-out opening portions 4.8' are alternately arranged in closely contacting relation, which are pressurized at a low pressure and a less volumetric flow rate such that the supporting operation of the air cushion substantially depends only on the viscosity of the air and sheet materials are just supported.