PURPOSE: To improve workability through easy and rapid manufacture of stairs of commercial quality by providing a manufacturing device consisting of a base approximately in a T-shape in longitudinal section, a pair of outer forms integrally molded in a shape matched with the outline of stairs, and a distance holding jig.

CONSTITUTION: Outer forms 3 and 3 made of a steel integrally molded in a shape matched with the uneven surface shape of the outline of stairs to be manufactured are disposed on both sides of the rise part of a longitudinally extending base 2 with a given distance therebetween. A separator 4 for an upper distance holding member is disposed near the external chevron apex of the outer forms 3, and a lower distance holding jig consisting of an L-shaped hardware, a nut, and a bolt is removably fixed at the forms 3 and the base 2. The upper and lower parts of the outer forms 3 are fastened against the base 2 by a distance holding jig 4. Concrete is placed in a space between the base 2 and the outer forms 3 to mold a pair of stairs in a given shape.