To easily hold and fix a frame on and to a bottom plate at its contacting surface on fabricating a low-framed handy food container by means of welding with a heating plate.

A frame member (a) made of foamed resin, with a thin bottom member (b) made of densified resin inserted therein, is suspended from a fixing jig 10, and a heated heating plate is pressed against joining parts of the frame and the bottom. With the jig 10 being used, the frame member (a) can be mounted on the frame of the jig 10 and the bottom member (b) can be fixed while being suspended with its upper edge contacted with the upper face of the frame member (a), and therefore a strong mechanical pressure is not applied to each of the members and welding can be executed smoothly on fabrication a low-framed handy food container.