Disclosed is a mashed potato that permits ingestion as much as that adaptable to fully demonstrate functional properties of konjak mannan to be attained, and is rich in water retentiveness, shape maintainability and flavors or tastes etc. The mashed potato according to the present invention is characterized in that addition of konjak mannan containing not less than 50% by weight of konjak mannan components to mashed potato dough is required, and no addition of a coagulant is required. An average particle size of the konjak mannan is not more than 177 .mu.m. A blend of about 100 or more parts by weight of water per one part by weight of konjak mannan is prepared, and the amount of konjak mannan added is in the range of 0.2 to 30% by weight.