To permit the arch of the foot to be constantly brought into contact by an elastic spring material and to be stimulated and to adjust stepping force so as to impart a flexibility to stimulation by installing the spring material with rugged projections in a part with which the arch of the foot of the shoe is brought into contact.

A plate 1 and a piece of bent plate 2 which are made of spring steel as a material are fixed by an adhesive, depositing or welding, etc., and some rugged projections 3 are fixed to the neighborhood of the top of the bent plate 2 by the adhesive. Moreover, the bottom surface of the plate 1 is fixed to a surface 4 where the arch of the foot of a sandal shoe is brought into contact by the adhesive or a screw, etc., Then, a cover 5 such as cloth or plastic is fitted in a whole part with which a sole is brought into contact so as to hide a spring. The spring material can be the one obtained by molding from resin such as plastic in addition to spring steel. The arch of the foot is stimulated by constant contact by the spring material with an elasticity by the configuration and the flexibility is imparted to stimulation by adjusting stepping force.