To simply and beautifully assemble an edge frame and to dispense with an adhesive to enhance sanitariness by forming mechanisms mutually slidable in the width direction of strip materials and engaged in the length direction and separating direction thereof to the opposed surfaces of both ends of the strip materials forming the edge frame.

After edge frame forming strip materials 3 are bent, half cut surfaces 6, 7 are formed to both end parts 4, 5 of the opposed strip materials and a wedge-shaped projection 8 and a wedge-shaped grooves 9 are formed to both end parts in the width direction of the central parts thereof and blade- shaped leading ends 10, 11 are formed toward the insides in the width direction of both end parts. The grooves 13, 12 receiving the blade-shaped leading ends 10, 11 are formed to the base parts of the half cut surfaces 4, 5 and both end parts 4, 5 are slid in a mutually fitted state to fit the wedge-shaped projection 8 in the wedge-shaped groove 9. By this constitution, both end parts 4, 5 are simply and certainly joined without using an adhesive or other adhesive structure to form an edge frame not separating both end parts 4, 5.