PURPOSE: To prevent leakage of electrolytic solution with resulting enhancement of reliability, by forming a seal layer in a gap between the gasket and the negative core rod of a slim type lithium battery.

CONSTITUTION: A positive electrode 1 with a collecting body 1a having positive electrode active substance bound on its one side is provided in a positive electrode case 6, opposing via a separator 4 to a negative electrode 2 comprising a lithium metal wound around a negative electrode core rod 3, and a slim type lithium battery is formed after sealing. In this formation, a seal layer 8 composed of a mixture of non-drying mineral oil or the like containing pitch as a main component or silicon oil or the like is provided in the gap (a) between a gasket 5 and the negative core rod 3 located at the sealing part. Consequently, leakage of electrolytic solution is prevented effectively, so that a high reliability battery can be obtained.