A bacterium is described which belongs to the Enterobacteriaceae family, and has an ability to produce an L-amino acid, such as L-glutamic acid, L-arginine and L-threonine. The bacterium is modified so that the activity of a protein encoded by ydcI gene is decreased, thereby producing and accumulating the L-amino acid selected from L-glutamic acid, L-arginine, and L-threonine in the culture medium or cells of the bacterium when cultured in a culture medium. Subsequently, the L-amino acid is collected from the culture medium or the bacterium.