To produce an Al alloy sheet excellent in formability, zinc phosphate treatability or the like with good productivity by subjecting a steel material of an Al-Mg base alloy contg. a specified amt. of Mg or the like to continuous heat treatment and surface treatment, thereafter executing low temp. heating treatment at a specified temp. and immediately coiling the same.

A sheet material S of an Al-Mg base alloy contg., by weight, 2 to 6% Mg, an Al-Mg-Si base alloy contg. 0.2 to 1.5% Mg and 0.1 to 1.6$ Si or an Al-Cu-Mg base allay contg. 0.6 to 3% Cu and 0.3 to 1.5% Mg is fed from a recoiling device 1 to a heating zone 4 and cooling zone 5, and is continuously subjected to heat treatment. Next, coating is removed with an alkali soln. or an acid soln. by a surface oxidized coating removing device 7 and, after that, it is continuously subjected to low temp. heating treatment at 40 to 120°C by a low temp. heating device 9 and is immediately coiled as a coil C by a coiling device 10. Thus, the Al alloy sheet excellent in coating/baking hardenability or the like can be obtd. using the same treating line.