A method for forming an undercut portion of a formed article formed by plastically deforming a plate-shaped workpiece and a method for manufacturing a formed article having an undercut portion are provided. In these methods, the undercut portion is formed by press working performed using a punch and a die. These methods make the forming work more economical and more efficient. An outer portion of a plate member 91 (plate-shaped workpiece) located outward of a portion where an inwardly inclined portion 94 (undercut portion) is to be formed is bent by an angle determined such that an undercut surface 94a which constitutes the inwardly inclined portion 94 becomes parallel to the pressing direction of a punch 110. In addition, a peripheral wall portion 93 inclined by an angle corresponding to the bending angle is formed on the outer portion. The bent portion of the plate member 91 having the inclined peripheral wall portion 93 is bent back in the opposite direction so as to cause the inwardly inclined portion 94 to rise up from the surface of the plate member 91.