To produce fluorescent bodies providing high brightness and high energy efficiency, a method of preparing a fluorescent body precursor is provided to enable an activator having a large ionic radius to be doped arbitrarily. The problems described above are solved by a method of preparing a fluorescent body precursor, which method is characterized by comprising applying a shock pressure of 0.1 GPa or higher to a mixture consisting essentially of a fluorescent body base, an activator and a co-activating particle-growth promoter to dope the activator into the fluorescent body base in the presence of the co-activating particle-growth promoter.