There is provided a manufacturing method of a hollow composite magnetic member having weakened magnetism in a portion of a ferromagnetic hollow member, the method includes: a step of forming a weak-magnetic area having weakened magnetism by melting and mixing a Ni-containing material and the hollow member by continuously supplying the Ni-containing material to a portion of the hollow member and heating the irradiation area having a line segment shape with the laser beam. Accordingly, since it is possible to prevent drop of a local portion of a hollow ferromagnetic pipe from being easily generated by a weak-magnetization treatment, to greatly reduce deformation generated by laser irradiation, and it becomes unnecessary to adjust the shielding gas pressure inside the pipe, the weak-magnetization treatment can be performed with higher efficiency and higher quality.