Abstract: A supporting device includes a suction base having a central base body interconnecting opposite suction units operable between non-sucking and sucking states. A supporting unit includes a rod-mounting seat having a connecting end portion disposed in a pivot groove in a top side of the central base body and connected pivotally to the central base body, and a mounting end portion disposed outwardly of the pivot groove and mounted rotatably with a supporting rod therein. The rod-mounting seat is positioned adjustably at a desired angular position relative to the central base body. A gun-mounting unit is mounted on the supporting rod, and is mounted with an air spray gun thereon.