Pouch Type Secondary Battery

A secondary battery including a terrace portion formed along a perimeter of an accommodation portion of an outer casing and having a sealing portion with a portion of a width thereof sealed a lead film disposed between and electrode lead and the outer casing, a gas guide portion disposed between the electrode lead and the lead film and including a permeable portion on an outer side of the sealing portion and a gas channel extending from the permeable portion toward the electrode assembly via the sealing portion. A reinforcing film on the lead film to covers a portion of the permeable portion. The reinforcing film includes an insertion portion occupying a portion of the width of the sealing portion, and the insertion portion is a region in which one end of the reinforcing film extends in an inward direction and is inserted between the outer casing and the lead film.