The modifying powder is silk powder having an average particle diameter of 10 μm or less, oil absorption of 130 ml/100 g or less and particle diameter of 80 μm or less on the basis of dispersion degree evaluation with a grind gauge according to JIS K5400; or polysaccharide powder having an average particle diameter of 10 μm or less, and ink viscosity of less than 15 Pa·s or oil absorption of 85 ml/100 g or less. Such modifying powders can be obtained through a method comprising a first pulverization process for pulverizing a starting material for modifying material using a dry-type mechanical pulverizer such as a ball mill, and a second pulverization process for pulverizing the obtained pulverized product with a jet mill to fine particles having an average particle diameter of 10 μm or less, wherein pulverization treatment time in the first pulverization process is determined to be 40 hours or more.