To obtain a quality improving agent to provide bread having springiness unlike that of conventional bread, excellent in crisp feeling, moisture retention, juiciness and keeping quality, causing no deterioration of palate feeling or appearance due to heating using a microwave oven after frozen, and also adaptable to intention for natural, healthy or genuine thing.

This quality improving agent comprises green or yellow Polymniosonchifolia squeezed juice obtained by processing Polymniosonchifolia root tuber which originally comes from Andean territory and is obtained through organic cultivation with no agrochemicals under specific conditions. The quality improving agent is added to bread dough, and the resultant dough is kneaded by well-known sponge and dough method or direct method, fermented and then baked.