It is intended to provide a bread improving agent with which bread having an improved fermented flavor and an improved texture can be produced within a short period of time, and a process for producing breads by using the same. It is found out that by adding fermented soybean protein, which is obtained by preliminarily fermenting soybean protein such as soybean milk with the use of a yeast, to a bread dough, the resulting baked bread has an extremely favorable fermented flavor and a preferable and soft texture maintained over a long period of time without taking a long time for the fermentation.