The effect of $CO_2$ concentration (500, 3,000, $6,000{mu}{ell}/{ell}$) on the mycelial growth and fruit body primordium formation of Ganoderma lucidum on nutrient agar medium was examined. Optimum $CO_2$ concentration for vegetative growth was above $3,000{mu}{ell}/{ell}$. Fruit body initiation was accelerated at higher than $3,000{mu}{ell}/{ell}$ $CO_2$ exposure but the maximum number and size of primordia, and primordium color were not influenced by $CO_2$ concentrations. Whereas each atypical fruiting structure forming stock culture showed different fruiting time under each concentration of $CO_2$ exposure.