Solid state battery

A solid state battery comprising:

• a battery element body including a positive electrode layer and a negative electrode layer laminated with a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer, the battery element body defining a first end surface and a second end surface facing each other, and a peripheral surface between the first end surface and the second end surface;
• a first external electrode on the first end surface;
• a second external electrode on the second end surface;
• and
• a protective layer covering only the peripheral surface of the battery element body,
• the solid state battery defining a first principal surface and a second principal surface facing each other in a lamination direction of the positive electrode layer and the negative electrode layer,
• wherein the first external electrode covers the first end surface and covers a side of the first end surface of the peripheral surface of the battery element body via the protective layer,
• the second external electrode covers the second end surface and covers a side of the second end surface of the peripheral surface of the battery element body via the protective layer, and
• at least one of the first principal surface and the second principal surface include a pair of a first convex part and a second convex part, each of which extend continuously from the first external electrode to the second external electrode along a longitudinal direction connecting the first external electrode and the second external electrode and located at opposed end parts of the solid state battery in a transverse direction to the longitudinal direction.