PURPOSE: To provide a separator capable of increasing the retainability of an electrolyte, decreasing partial drying and localization of electrode reaction, making use of an excessive amount of the electrolyte unnecessary in assembly of a lithium secondary battery, and making components such as electrode material for accommodating in the battery large when battery sizes are equal.

CONSTITUTION: A separator comprises a coating film 1 made of a polymer having a chemical structure part with high affinity with a solvent of an electrolyte and a porous insulating film 2. A positive electrode layer is arranged on one side of the separator 3 and a negative electrode layer is on the other side. By this constitution, the decrease in battery performance caused by forming of the coating film is avoided, and the separator with high electrolyte absorbing capability, and high retainability of the absorbed electrolyte caused by the coating film to make leakage difficult can be obtained.