A cab for use in a construction machine including a lower travelling body and an upper slewing body slewably mounted on the lower travelling body, the upper slewing body including an upper frame, the cab being disposed on one of right and left side portions of the upper frame, the cab comprising: a pair of rear pillars (21, 22) standing in a rear portion of the cab and laterally spaced; and a rear panel disposed between the pair of rear pillars (21,22), wherein: the rear panel includes an outer panel and an inner panel disposed on an inner side of the outer panel and joined to the outer panel; the inner panel includes a plurality of panel portions (31, 32) vertically arranged, each of the panel portions (31, 32) extending laterally, each of the plurality of panel portions (31, 32) is formed of a plate member, and an upper edge portion and a lower edge portion of the plate member are bent so as to form respective upper and lower reinforcement edge portions (31a, 32a, 31b, 32b); characterized in that the inner panel includes a bridge portion partly bridging the panel portions (31, 32) vertically adjacent to each other, at a position offset outward in a width direction of the upper frame from a lateral center position of the rear panel; the bridge portion is a plane plate having no bending portion; the bridge portion forms a low-strength portion of the inner panel, the low-strength portion having a lower strength than a strength of the panel portions (31, 32) against a lateral load applied to the rear panel through an outer rear pillar of the pair of rear pillars (21, 22) from outer side widthwise of the upper frame upon turning over of the construction machine, so as to make the low-strength portion include a bending point at which the rear panel is bent by the lateral load; and the upper reinforcement edge portions (31a, 32a) and the lower reinforcement edge portions (31b, 32b) of the panel portions (31, 32) are secured to the outer panel, while the bridge portion is independently separated from the outer panel. a pair of rear pillars (21, 22) standing in a rear portion of the cab and laterally spaced; and a rear panel disposed between the pair of rear pillars (21,22), wherein: the rear panel includes an outer panel and an inner panel disposed on an inner side of the outer panel and joined to the outer panel; the inner panel includes a plurality of panel portions (31, 32) vertically arranged, each of the panel portions (31, 32) extending laterally, each of the plurality of panel portions (31, 32) is formed of a plate member, and an upper edge portion and a lower edge portion of the plate member are bent so as to form respective upper and lower reinforcement edge portions (31a, 32a, 31b, 32b); characterized in that the inner panel includes a bridge portion partly bridging the panel portions (31, 32) vertically adjacent to each other, at a position offset outward in a width direction of the upper frame from a lateral center position of the rear panel; the bridge portion is a plane plate having no bending portion; the bridge portion forms a low-strength portion of the inner panel, the low-strength portion having a lower strength than a strength of the panel portions (31, 32) against a lateral load applied to the rear panel through an outer rear pillar of the pair of rear pillars (21, 22) from outer side widthwise of the upper frame upon turning over of the construction machine, so as to make the low-strength portion include a bending point at which the rear panel is bent by the lateral load; and the upper reinforcement edge portions (31a, 32a) and the lower reinforcement edge portions (31b, 32b) of the panel portions (31, 32) are secured to the outer panel, while the bridge portion is independently separated from the outer panel. the rear panel includes an outer panel and an inner panel disposed on an inner side of the outer panel and joined to the outer panel; the inner panel includes a plurality of panel portions (31, 32) vertically arranged, each of the panel portions (31, 32) extending laterally, each of the plurality of panel portions (31, 32) is formed of a plate member, and an upper edge portion and a lower edge portion of the plate member are bent so as to form respective upper and lower reinforcement edge portions (31a, 32a, 31b, 32b); characterized in that the inner panel includes a bridge portion partly bridging the panel portions (31, 32) vertically adjacent to each other, at a position offset outward in a width direction of the upper frame from a lateral center position of the rear panel; the bridge portion is a plane plate having no bending portion; the bridge portion forms a low-strength portion of the inner panel, the low-strength portion having a lower strength than a strength of the panel portions (31, 32) against a lateral load applied to the rear panel through an outer rear pillar of the pair of rear pillars (21, 22) from outer side widthwise of the upper frame upon turning over of the construction machine, so as to make the low-strength portion include a bending point at which the rear panel is bent by the lateral load; and the upper reinforcement edge portions (31a, 32a) and the lower reinforcement edge portions (31b, 32b) of the panel portions (31, 32) are secured to the outer panel, while the bridge portion is independently separated from the outer panel.