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, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer; first and second external terminals joined to an extended portion of each electrode layer of the positive electrode layer and the negative electrode layer, respectively; and a protective layer that covers a surface of the battery element other than the extended portions of each electrode layer, the protective layer including a side portion on a central region of a side portion of the battery element extending in substantially the same direction as the stacking direction and in which a first thickness dimension of a first portion is larger than a second thickness dimension of a second portion other than the first portion.