PURPOSE: To obtain a thin film solid electrolyte having a high ionic conductivity and a great discharge current by carrying out vapor deposition using a mixture consisting of lead fluoride and lithium fluoride as a vapor deposition source.

CONSTITUTION: Either a mixture powder consisting of lead fluoride powder and lithium fluoride powder or a pellet obtained by fusing and cooling the above mixture powder is used as an evaporation source. The evaporation source is vapor-deposited on a base plate by a resistance heating method or an electrobeam method to make a thin film solid electrolyte. By the means mentioned above, an anode electrode, a solid electrolyte and a cathode electrode can be formed by a vapor deposition method as thin films. In a battery constituted by use of this thin film solid electrolyte, a high discharge current can be achieved even after continuous discharging.