An all-solid-state battery includes a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The solid electrolyte layer separates the positive electrode layer from the negative electrode layer. The positive electrode layer includes a positive electrode active material, a conductive material, an oxide-based lithium ion conductor, and a sulfide-based solid electrolyte. A cross section of the positive electrode layer satisfies a relational expression (1): 3%≤SB/SA≤30%. In the relational expression (1), “SA” represents a partial area of the oxide-based lithium ion conductor that is in contact with the positive electrode active material, and “SB” represents a partial area of the oxide-based lithium ion conductor that is surrounded by the sulfide-based solid electrolyte.