A mounting structure of a sheet metal panel including mounting brackets which are mounted on a peripheral edge portion of a glass-mounting opening formed on a rear-side panel of a cab, and after tentatively holding the sheet metal panel, a peripheral edge of the sheet metal panel is adhered to the rear-side panel in a periphery of the glass-mounting opening, wherein an inclined surface protruding toward a rear of the cab is provided to the rear-side panel along the glass-mounting opening, and the peripheral edge of the sheet metal panel is bent along the inclined surface and extended in the inclined surface direction to make clearance between the peripheral edge and the inclined surface gradually narrowed, to provide an adhesive reservoir between the sheet metal panel and the rear-side panel, and the peripheral edge of the sheet metal panel is in close contact with the inclined surface thereby sealing therebetween.