PURPOSE: To transfer respective forming dies and take out respective fusion bonding boxes quickly and securely and improve the quality by separating a plurality of box manufacturing section from discharge sections and connecting a plurality of forming dies so that respective sections are adjoining at corresponding intervals.

CONSTITUTION: A box manufacturing device consists of box manufacturing sections 2, discharge sections 3 and a moving mechanism 6 in addition to a sheet stack mechanism 1 feeding sheets S of synthetic resin as main constituting sections. Fusion bonding boxes B of the box manufacturing sections 2 are assembled and formed from the sheets S by a plurality of movable forming dies 5 (a, b), and the sheets S are formed into the unfolded box shape by a hot blade 21, and the sheets S of unfolded box shape is pressed into the forming dies 5 by pressing mechanisms 24 and 26. Also the fusion bonding boxes 3 are taken out by extrusion mechanisms 31 (a, b) and 32 (a, b) of the discharge sections 3. The forming dies 5 are moved to the discharge sections 3 by the moving mechanism 6. The forming dies 5 are connected so as to adjoin one another at the interval corresponding to the box manufacturing sections 2 and the discharge sections.