Abstract: A thin, forged magnesium alloy casing is integrally constituted by a thin plate with projections on either or both surfaces, and the thin plate is as thin as about 1.5 mm or less. The thin forged casing can be produced by (a) carrying out a first forging step for roughly forging a magnesium alloy plate to form an intermediate forged product under the conditions of a preheating temperature of the magnesium alloy plate of 350-500° C., a die temperature of 350-450° C., a compression pressure of 3-30 tons/cm2, a compressing speed of 10‥500 mm/sec. and a compression ratio of 75% or less; and (b) carrying out a second forging step for precisely forging the intermediate forged product under the conditions of a preheating temperature of the intermediate forged product of 300-500° C., a die temperature of 300-400° C., a compression pressure of 1-20 tons/cm2, a compressing speed of 1-200 mm/sec., and a compression ratio of 30% or less.