To make it possible to increase the strength of the suitcase of a rigid frame having casters and retractable handle and to decrease the weight thereof.

This structure is made of a rigid frame assembly structure including a front panel 12, a rear panel 14 and a shell attaining the shape of a C-shaped bottom panel 19. This rigid frame assembly structure is assembled by extrusion of a plastic material, such as acrylonitrile-butadiene-styrene copolymer(ABS) or polyvinyl chloride(PVC). The respective panels are formed of cells which are segmented by ribs extending in a longitudinal direction and extend in the longitudinal direction. The front and rear panels are mounted to the C-shaped bottom panel by means of an integrally formed joining flange. The joining flange extends to engage the inner surface of the end panel part extending from the bottom panel in superposition thereon. The front and rear panels are mounted and fixed to one of the end panel parts by the supporting plate of a caster assembly structure.