A method of removing arsenic from water by using a reactor that is provided with a fluidized bed of carriers is disclosed. An arsenic-containing influent is mixed in the reactor with a sulfide aqueous solution or metallic salt aqueous solution at a predetermined pH, thereby resulting in formation of crystals of arsenic sulfides or arsenic acid metal salts. The arsenic contained in the influent is thus removed by crystallization. An effluent with a reduced arsenic content is discharged from the reactor. The carriers, on which the crystals are formed, are periodically removed from the reactor which is replenished with fresh carriers immediately after.