SOLID STATE BATTERY

A solid state battery that includes: a battery element including, along a stacking direction, one or more battery constituent units including a positive electrode layer and a negative electrode layer each having extended portions, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer; a first external terminal and a second external terminal that a respectively electrically connected to the positive electrode layer and the negative electrode layer; a protective layer covering a surface of the battery element; and a buffer portion surrounding at least one of the positive electrode layer and the negative electrode layer in the plan view, wherein at least a local portion of the buffer portion between a side surface of the electrode layer having the extended portion and the external terminal includes a resin-free insulating material substantially identical to a resin-free insulating material of the protective layer.