A device-supporting member configured to be provided in an upper slewing body of a working machine to support the device, comprising: an upper horizontal plate portion disposed substantially horizontally, the upper horizontal plate having an upper surface for placing the device (71; 73) thereon; a lower horizontal plate portion disposed substantially horizontally below the upper horizontal plate portion , the lower horizontal plate portion having a lower opening formed to penetrate therethrough in an up-and-down direction so as to allow maintenance of the device; and a first vertical plate portion and a second vertical plate portion each provided between the upper horizontal plate portion and the lower horizontal plate portion , wherein: the upper horizontal plate portion , the first vertical plate portion , the lower horizontal plate portion and the second vertical plate portion are arranged to define a closed cross-section when viewed in side view; and an upper opening includes a horizontal opening formed in the upper horizontal plate portion in a region approximately overlapping the maintenance hole in top plan view, and a vertical opening formed in the first vertical plate portion in continuous relation with the horizontal opening so as to allow the maintenance of the device (71; 73) through the lower opening and the upper opening . an upper horizontal plate portion disposed substantially horizontally, the upper horizontal plate having an upper surface for placing the device (71; 73) thereon; a lower horizontal plate portion disposed substantially horizontally below the upper horizontal plate portion , the lower horizontal plate portion having a lower opening formed to penetrate therethrough in an up-and-down direction so as to allow maintenance of the device; and a first vertical plate portion and a second vertical plate portion each provided between the upper horizontal plate portion and the lower horizontal plate portion , wherein: the upper horizontal plate portion , the first vertical plate portion , the lower horizontal plate portion and the second vertical plate portion are arranged to define a closed cross-section when viewed in side view; and an upper opening includes a horizontal opening formed in the upper horizontal plate portion in a region approximately overlapping the maintenance hole in top plan view, and a vertical opening formed in the first vertical plate portion in continuous relation with the horizontal opening so as to allow the maintenance of the device (71; 73) through the lower opening and the upper opening . the upper horizontal plate portion , the first vertical plate portion , the lower horizontal plate portion and the second vertical plate portion are arranged to define a closed cross-section when viewed in side view; and an upper opening includes a horizontal opening formed in the upper horizontal plate portion in a region approximately overlapping the maintenance hole in top plan view, and a vertical opening formed in the first vertical plate portion in continuous relation with the horizontal opening so as to allow the maintenance of the device (71; 73) through the lower opening and the upper opening . <EOS>