A composite porous separator includes: a porous substrate acting as a support and having a first melting point and a first porosity; a first porous polymer web layer that is laminated on one side of the porous substrate, and acts as an adhesive layer when being in close contact with an opposing electrode; and a second porous polymer web layer that is laminated on the other surface of the porous substrate, and is formed of nanofibers of a heat-resistant polymer, in which the first porous polymer web layer and the second porous polymer web layer have a melting point higher than the first melting point of the porous substrate and a porosity that is the same as or similar to the first porosity of the porous substrate, respectively.