PURPOSE: To efficiently obtain an expanded material having a square shaped opening, by forming an intermediate formed part having many hexagonal openings from a stock constituted of a web for connecting adjacent cords, fitting and covering rupture preventing fittings to said part, and expanding it.

CONSTITUTION: An extruded shape is constituted of parallel-shaped cords 2 and a web for connecting adjacent cords, and in each web thereof, many slots are made so as to be placed zigzag, and the extruded shape is drawn and expanded in the width direction. In this way, an expanded intermediate formed part 11 having many hexagonal opening 5 is obtained. Subsequently, a rupture preventive metallic fixture 6 is fitted and covered to all the remaining webs 3a and cored parallel straight line parts 2a, 2a of the intermediate formed part 11, and also, said part is stretched and expanded to the right and left, and inclined parts 2b, 2b of the cord 2 are bent vertically against the parallel straight line parts 2a, 2a. In this way, a metallic expanded material having a square-shaped opening can be obtained efficiently.