A battery pack includes a plurality of battery cells each including a laminate film casing from which positive and negative electrode lead tabs are led out in a same direction, and a coupling assisting member that includes a conductive plate member fixing portion that fixes a conductive plate member having first and second main surfaces, and first and second slit portions provided on the first and second main surface sides of the conductive plate member, respectively. Either of the positive and negative lead tabs of one battery cell is inserted through the first slit portion and conductively connected to the first main surface. A lead tab of a battery cell adjoining one battery cell and having a polarity different from that of the lead tab of the one battery cell, is inserted through the second slit portion and conductively connected to the second main surface.