To dispense with ensuring a release port for steam prior to a heat-cooking by providing an extended heat-bonded section having an easy peelability, which is heat-bonded in a manner to be extended to the inside from the internal edge, at specified locations on the internal edge of both side sections being heat-bonded between an engaging device and a bottom section folded-in section, and forming a cutting blade or a notch in the extended heat-bonded section.

An approx. trapezoidal extended heat-bonded section 5 having an easy peelability which is heat-bonded in such a manner that the extended heat-bonded section 5 is connected to the internal edge of both side end heat-bonded sections 50 between an engaging device 4 and a bottom section folded-in section 3, and is extended to the inside, is formed. Also, in the extended heat-bonded section 5, a plurality of semi-circular notches 6 are provided in a manner to go through the confronted front and rear wall sections of the extended heat-bonded section 5. By this constitution, by the provision of the extended heat-bonded section 5 having easy peelability, the internal pressure in a pouch 1 can be automatically released from the notches 6 provided on the extended heat-bonded section by making it separate quicker than other heat-bonded sections by the internal pressure. Therefore, the ensuring of a release port for steam prior to a heat-cooking is not reguired, and also, the pouch 1 is prevented from exploding.