According to one embodiment, a composite electrolyte includes lithium-containing oxide particles and an electrolytic composition. The electrolytic composition includes lithium ions, an organic solvent and a polymer. A content of the lithium-containing oxide particles in the composite electrolyte falls within a range of from 90% by weight to 98% by weight. A specific surface area of the lithium-containing oxide particles falls within a range of 10 m2/g to 500 m2/g and is measured by a BET adsorption method using N2.