An inexpensive packaging pouch for use in a microwave oven, in which the packaging pouch can be prevented from opening at the base part of a branch section when used for retorting or for cooking in the microwave oven, and pressure in the packaging pouch can be automatically released when the pouch is used for cooking in the microwave oven. A packaging pouch for microwave oven hermetically sealed by heat-sealing a plastic film is provided with a branch section, and a vapor release seal part having at least one weakened part is formed at the branch section. Opening preventive means are provided at the branch section and inside a peripheral edge seal part, facing the branch section, of a packaging pouch body.