To provide a friction stir welding method for an aluminum member in which deformation of a welding member can be effectively suppressed or prevented while highly securing bonding strength of the welding member to be obtained by welding, and the aluminum member which is advantageously used for such a friction stir welding method.

The friction stir welding is executed by using a material in a shape of which the place adjacent and positioned to a stir welding part to be formed at an abutting part 16 of a sheet-like part 12a is made thicker than a base material part at a prescribed width, and the place 22a on the abutting part 16 side from such a thick-walled place 14a is made thinner than the thick-walled place 14a as the aluminum member 10a.