A check-valved pouch has a main pouch body, and a check valve attached to the main pouch body. The main pouch body is formed of plastic film and defines an opening for receiving a substance. The check valve is formed of plastic film also, and includes a flat valve body defining an upper opening, with opposte sides and a lower end closed, and an inner passage for discharging gases toward the upper opening. A check piece formed of plastic film is disposed in an upper half of the valve body. The check valve further includes a porous filtering film disposed on one surface in a lower half of the valve body. The filtering film includes a filter surface, and a releasing film formed on the filter surface. The check valve is attached to the main pouch body, with the filtering film inserted into the main pouch body and the upper opening exposed to ambient air, whereby an interior of the main pouch body is communicable with an exterior through the filter surface, inner passage and upper opening.