A method of manufacturing a powder, by which it is possible to adjust the strength of the obtained powder is provided. The manufacturing method of a powder involves a step of preparing a slurry containing agglomerated particles of a synthetic material which is produced by reacting a first material and a second material under agitation, and a step of drying the slurry to obtain a powder of the synthetic material. The method has a feature that the particle size of the agglomerated particles is adjusted by, in the step of preparing a slurry, controlling agitation power for agitating the slurry. In the step of preparing a slurry, it is preferable that the slurry is initially agitated at a first agitation power, and at the time when the viscosity of the slurry approaches its maximum value, or at the time when the pH value of the slurry reaches the vicinity of the isoelectric point of the synthetic material, the agitation power is lowered from the first agitation power to a second agitation power. Further, it is preferable that before or after the completion of the reaction of the first material and the second material, the agitation power is increased from the second agitation power to a third agitation power.