A technology for producing a pig edema disease vaccine at low cost and at high efficiency is developed. Specifically, a gene of a pig edema disease toxin protein (Stx2e protein) is efficiently expressed in plant cells to produce a plant vaccine for pig edema disease at low cost. An Stx2e protein including a secretory signal peptide derived from a plant added at an amino terminus is expressed in cells of a plant such as Lactuca sativa using the 5′-untranslated region of an alcohol dehydrogenase gene (ADH5′UTR) derived from a plant.