All-solid-state lithium–sulfur batteries are expected to be valuable next generation batteries. To improve the performance of all-solid-state lithium–sulfur batteries, it is essential to raise both the reactivity of sulfur and the ionic conductivity of the positive composite electrode. For achieving this, we investigate a positive composite electrode prepared using P2S5 and a solid electrolyte with a high ionic conductivity. As a result, we have found that the lithium–sulfur cell exhibits a relatively low activation energy together with high ionic conductivity. The positive composite electrode exhibits an extremely high capacity of 1550 mA h g−1 (sulfur) at 1.3 mA cm−2 and 25 °C. Moreover, when using the positive electrode, the energy densities at the cell level (18650) are 540 W h kg−1 and 990 W h L−1, estimated from the equivalent structure of a current lithium-ion battery.