The invention discloses a varnish coating device that utilizes an ordinary conventional digital stencil printing apparatus, such that anyone can easily apply a uniform film of a viscous coating onto a predetermined area of, for instance, covers and surfaces of printed products. The invention functions as a varnish coating device, in place of a drum unit, when a varnish coating unit is mounted on a mounting section of a printing apparatus main body. The varnish coating unit has: a coating roller that coats the surface of printed paper with a transparent varnish liquid and feeds out the paper; a supply device having a doctor roller that forms a liquid pool on the coating roller and that supplies varnish liquid to form a coating in a predetermined thickness over a predetermined area of the surface of the coating roller; a cradle that detachably supports a varnish container; and a pumping device.