Disclosed herein is a method of sealing a side portion of a pouch-shaped battery including an electrode current collector and a pouch-shaped battery case, the method including bending a lower case and an upper case connected to the lower case such that the upper case faces the lower case and the electrode current collector is disposed in the lower case, the lower case and the upper case being connected to one another at a bent portion of the pouch-shaped battery case, a primary sealing step of sealing the lower end part of the side portion of the pouch-shaped battery case adjacent to the bent portion of the pouch-shaped battery case, and a secondary sealing step of sealing the entirety of the side portion of the pouch-shaped battery case.