Method for adding sweet, fragrant soybean flavor to natto

The purpose of the present invention is to provide a technology applicable in general to Bacillus natto and whereby an excellent flavor completely different to conventional natto (fermented soybeans), from a flavor viewpoint, can be added to natto. Provided is a method for adding a sweet, fragrant soybean flavor to natto, characterized by, after inoculating steamed or boiled soybeans with Bacillus natto, performing: a step (1) in which the temperature of the soybeans is substantially maintained at 37-53°C and the soybeans are fermented, for 5.5-14.5 hours; and a step (2) in which after performing step (1), the temperature of the soybeans is substantially maintained at 55-70°C and the soybeans are heat treated, for up to 3.5 hours. Also provided is natto having: a property (a) whereby the acetoin content per 100 g natto (wet weight) is at least 150 mg; and a property (b) whereby the guaiacol content per natto (wet weight) is at least 1.5 ppm.