PURPOSE: To enhance storage stability, solubility, processing stability, handleability, social environment aptitude, and operation environment aptitude by incorporating a specified compound.

CONSTITUTION: This processing agent has a bulk density of ≥1.2g/cm3 and contains at least one of the compounds represented by formula I in which each of X1, X2, Y1, and Y2 is hydroxy, halogen, morpholino, alkoxy, aryloxy, alky, aryl, amino, alkylamino, or arylamino ; and M is H, an alkali metal, or the like. It is preferred that this agent is formed by granulating and pelletizing the material containing at least 3 kinds of granulates of a granulate containing an antioxidant, one containing a color developing agent, and one containing an alkali agent and pelletizing by compressing the mixture with pressure.