Abstract: Apparatus is provided for carrying out a varnish impregnation method wherein a sheet-like base material is sequentially passed through a low-viscosity liquid storage region storing a low-viscosity liquid such as a solvent, a thermal syphon region, and a varnish storage region storing a varnish, the thermal syphon region being positioned between the low-viscosity liquid storage region and varnish storage region and communicating with both regions at air tight seals closed by liquid surfaces, and heating the base material in the thermal syphon region to vaporize the low-viscosity liquid impregnated in the base material. When the base material passes through the low-viscosity liquid, air contained in the base material is replaced with the low-viscosity liquid and discharged outside the apparatus. The low-viscosity liquid impregnated in the material is vaporized in the thermal syphon region.