To provide a mixer drum in which a working man-hour is reduced and cost reduction is contrived and effect of stress caused by hardening of material in a joining part is reduced and durability is held by mutually lapping the respective shells, fixing and joining the shells by welding without forming a bending part in the end peripheral edges of the shells.

The drum 2 of a ready-mixed concrete car consists of an end plate 11 formed into a circular arc shape, the front shell 12 formed into a conical cylinder shape having a peripheral edge part 12A which is engaged with the end plate 11 and has small diameter and large diameter, a center shell 13 which is engaged with the front shell 12 and formed into a cylindrical shape and the rear shell 14 which is engaged with the center shell 13 and has largediameter and small-diameter peripheral edge parts 12A, 12B. In this drum 2, the front peripheral edge part of the center shell 13, the large diameter peripheral edge part 12A of the front shell 12, the rear peripheral edge part 13B of the center shell 13 and the large diameter peripheral edge part 12A of the rear shell 14 are lapped respectively mutually, fixed and joined from one side by welding.