To provide a packaging bag for food which is hard to be deformed even when an external force is applied to the corner section, and at the same time, is equipped with a good appearance; and its manufacturing method.

A pair of triangular side surface sections A, A are constituted of a composite film 1 comprising a rear surface with heat-sealability and a front surface without heat-sealability. A square front surface section C and a square back surface section B which bridge respective side edges E, E of a pair of the side surface sections A, A are constituted of a plastic film 2 with heat-sealability. Then, respective side edges E, E and so forth of the side surface sections A, A, the front surface section C and the back surface section B are heat-sealed. Thus, reinforced belt-like sealing sections 3, 3 and so forth are formed on respective side edges E, E.