Process for manufacturing modified starch. A powdery starch composition raw material, containing a specified amount of a phosphate with respect to a raw material starch on a dry basis, is subject to esterification modification by performing a first step of heat treating by raising a temperature gradually and performing, in continuation, a second step of heat treating at a constant temperature. A temperature rise starting temperature of the first step is set within a range from an ordinary temperature to a temperature no more than a gelatinization starting temperature of the raw material starch, a temperature rise rate is set to 0.2 to 1° C./min, and a temperature rise final temperature is set to 120 to 180° C. The constant temperature treatment is normally performed at the temperature rise final temperature.
