Abstract: A stamp and a process of producing a stamp includes a stamp that is made from a sponge having open cells to allow repeated impressing operations without supplying stamp ink for a long time. The process includes fitting a heat-fusing ink sheet or a heat-generating plate, which contains a heat-generating material, over the surface of a stamp-piece that has open cells therein. A liquid substance soaks a manuscript having characters, patterns, etc., which are represented by non-applied areas of recording material. The manuscript is placed over the top in such a manner that an image may appear to be a mirror image. The manuscript is irradiated from above with light to cause light to pass through the non-applied areas of recording material to increase the temperature of the heat-generating material at sites corresponding to the non-applied areas of recording material.