A rotary kiln includes a cylindrical shell that rotates about its own axis and that has a heat treatment chamber provided radially inward of the shell. In the rotary kiln, a heat treatment is performed on a process material in the heat treatment chamber to manufacture a battery material. The shell is made of a carbon material. Since the shell is made of a carbon material, the rotary kiln can suppress contamination of metal scale, which adversely affects the battery material, into the battery material.