The invention relates to a technique for activating an in vivo immune function by promoting IFN-? production using a bifidobacterium-fermented product of a Brassica plant and a technique for preventing or improving a disease caused by candida infection, for example, an allergic disease such as atopic dermatitis, candidiasis such as periodontal disease, dental caries, stomatitis, glossitis, oral infection, aspiration pneumonia or vaginitis. More particularly, it relates to an agent for preventing or improving a disease caused by candida infection containing a bifidobacterium-fermented product of at least one kind of plant selected from the group consisting of Brassica plants and carrot, an oral composition for preventing or improving a disease caused by candida infection, an immunostimulant and the like. Examples of the bifidobacterum include Bifidobacterum longum and the like. Examples of the plant which is at least one kind of plant selected from the group consisting of Brassica plants and carrot include broccoli, cabbage, kale, cauliflower, Brassica juncea var. integlifolia, oilseed rape, brown mustard, radish, radish leaves, Brassica rapa var. hakabura, Brassica rapa var. peruviridis and the like.
