Attempts were made to investigate the effects of the temperature and carbon dioxide concentration in the growing room and soil moisture after casing on the mycelial growth, sporophore formation and mushroom yield of Agaricus bisporus (Lange) Sing. The growing room temperature influenced the mycelial growth in the casing layer after casing and the sporophore formation of Agaricus bisporus. The mycelial growth was the rapidest at $30^{circ}C$ and gradually decreased with the temperature going down, while the sporophore formation and mushroom yield were the best at $25^{circ}C$. The other factor which affected the mycelial growth and sporophore formation was the moisture content of casing soil. The mycelial growth was the best at 70 percent moisture, and the sporophore formation and mushroom yields were the highest at 60 percent moisture. The concentration of carbon dioxide in the growing room after casing had an important effect upon the mycelial growth in the casing layer and the sporophore formation. When the concentration of carbon dioxide was 0.16 percent, the mycelial growth and the sporophore formation were not inhibited. At 0.5 to 2.0 percent $CO_{2}$ the myceilal growth and the sporophore formation were severely decreased. The sporophore size of the mushroom was the maximum when the room temperature during the vegetative mycelium growth was $20^{circ}C$ and the moisture content of casing soil was 70 percent.