An embossment formation area A is formed on one surface of envelope paper S. The embossment formation area A is left-right symmetric with respect to a centerline L including the centerline L parallel to a paper feed direction (transport direction), and is formed rearward over a predetermined length from a leading end in the paper feed direction. An embossment E has convexes that are equal in height to or higher than the thickness of transparent film Sc attached to a window Sa, that is, a thickness change portion S1. Even when many sheets of the envelope paper are stacked, the envelope paper can be fed without causing a double feed or a no-load feed.