An aluminum-alloy plate (10) equipped with an aluminum-alloy substrate (1) and an aluminum-oxide film (2) formed on the surface of the aluminum-alloy substrate (1), wherein: the aluminum-oxide film (2) contains at least one type of additional element having a P-B ratio of 1.00 or more, zirconium in the amount of 0.01-10 atomic percent, and magnesium in the amount of 0.1 or more and less than 10 atomic percent; and the total amount of additional elements contained in the aluminum-oxide film (2) is 0.010-5.0 atomic percent. As a result, it is possible to provide: an aluminum-alloy plate which exhibits excellent post-degreasing-water-wettability stability even when in a high-temperature, high-humidity environment; and a joined body and a vehicle member which use the same.