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 (16a, 16b) 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 (16a, 16b). 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 (16a, 16b) 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 (16a, 16b). 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 (16a, 16b) 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 (16a, 16b).