Mibyou has been defined in traditional oriental medicine as a certain physiological condition whereby an individual is not ill but not healthy; it is also often referred to as a sub-healthy condition. In a society focused on longevity, “Mibyou-care” becomes of primary importance for healthy lifespan expenditure. Functional foods can play crucial roles in Mibyou-care; thus, the search for novel resources of functional food is an important and attractive research field. Mushrooms are the target of such studies because of their wide variety of biological functions, such as immune modulation and anti-obesity and anticancer activities, in addition to their nutritional importance. Basidiomycetes-X (BDM-X; Shirayukidake in Japanese) is a mushroom which has several attractive beneficial health functions. A metabolome analysis revealed more than 470 components of both nutritional and functional interest in BDM-X. Further isolation and purification studies on its components using radical scavenging activity and UV absorbance identified ergosterol, (10E,12Z)-octadeca-10,12-dienoic acid (CLA), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP), formyl pyrrole analogues (FPA), including 4-[2-foemyl-5-(hydroxymethyl)-1H-pyrrole-1-yl] butanamide (FPAII), adenosine and uridine as major components. Biological activities attributed to these components were related to the observed biological functions of BDM-X, which suggest that this novel mushroom is a useful resource for Mibyou-care functional foods and medicines.