A solid electrolyte battery having improved energy density and safety, the solid electrolyte battery incorporating a positive electrode; a negative electrode disposed opposite to the positive electrode; a separator disposed between the positive electrode and the negative electrode; and solid electrolytes each of which is disposed between the positive electrode and the separator and between the separator and the negative electrode, wherein the separator is constituted by a polyolefin porous film, the polyolefin porous film has a thickness satisfying a range not greater than 5 .mu.m nor greater than 15 .mu.m and a volume porosity satisfying a range not less than 25% nor greater than 60%, and the impedance in the solid electrolyte battery is greater than the impedance realized at the room temperature when the temperature of the solid electrolyte battery satisfies a range not less than 100.degree. C. nor greater than 160.degree. C.