A cylindrical lithium-ion battery with high safety, high capacity and high power has a winding group having a positive electrode, a negative electrode and at least one separator, and a connecting portion for connecting to respective terminals from the winding group accommodated in a battery container, and which is provided with an inner pressure-reducing mechanism for discharging gas according to an increase in inner pressure inside the battery container. The positive electrode includes a collector whose both surfaces are applied with composing material including lithium-manganese complex oxide, the thickness of the composing material on the both surfaces of the collector is at least 210 &mgr;m and the amount of the active material per one surface of the collector is at least 240 g/m2. The compounding ratio of the lithium-manganese complex oxide in the composing material is preferably at least 80 wt %.