A package bag having: a flexible main package bag body formed by fusion-joining a sealant layer of a packaging film of laminated structure including a base film layer and the sealant layer; and a one-way pouring nozzle having a self-sealing function formed by fusion-joining a portion around a pouring path of in-bag material to be packaged without a base end side, which is constructed by a planar laminated film having thin thickness comprising sealant layers on front-back both sides, comprising: a projection portion of the packaging film extending continuously from the flexible main package bag body, with which the whole one-way pouring nozzle is covered from both of a front surface side and a back surface side; and a tear-inducing flaw, characterized in that the tear-inducing flaw is formed in the projection portion and extends across a center portion of the projection portion in a projection direction of the one-way pouring nozzle from the flexible main package bag body; the one-way pouring nozzle is projected laterally from an upper portion or a lower portion of the flexible main package bag body by fusion-joining an outer surface of a base end portion of the one-way pouring nozzle to the sealant layer existing on an inner surface of a side portion of the main package bag body; and the main package bag body comprises an upper opening or a lower opening whereby the main package bag body can be opened at either one side of an upper end or a lower end for filling a liquid material to be packaged. a flexible main package bag body formed by fusion-joining a sealant layer of a packaging film of laminated structure including a base film layer and the sealant layer; and a one-way pouring nozzle having a self-sealing function formed by fusion-joining a portion around a pouring path of in-bag material to be packaged without a base end side, which is constructed by a planar laminated film having thin thickness comprising sealant layers on front-back both sides, comprising: a projection portion of the packaging film extending continuously from the flexible main package bag body, with which the whole one-way pouring nozzle is covered from both of a front surface side and a back surface side; and a tear-inducing flaw, characterized in that the tear-inducing flaw is formed in the projection portion and extends across a center portion of the projection portion in a projection direction of the one-way pouring nozzle from the flexible main package bag body; the one-way pouring nozzle is projected laterally from an upper portion or a lower portion of the flexible main package bag body by fusion-joining an outer surface of a base end portion of the one-way pouring nozzle to the sealant layer existing on an inner surface of a side portion of the main package bag body; and the main package bag body comprises an upper opening or a lower opening whereby the main package bag body can be opened at either one side of an upper end or a lower end for filling a liquid material to be packaged. a projection portion of the packaging film extending continuously from the flexible main package bag body, with which the whole one-way pouring nozzle is covered from both of a front surface side and a back surface side; and a tear-inducing flaw, characterized in that the tear-inducing flaw is formed in the projection portion and extends across a center portion of the projection portion in a projection direction of the one-way pouring nozzle from the flexible main package bag body; the one-way pouring nozzle is projected laterally from an upper portion or a lower portion of the flexible main package bag body by fusion-joining an outer surface of a base end portion of the one-way pouring nozzle to the sealant layer existing on an inner surface of a side portion of the main package bag body; and the main package bag body comprises an upper opening or a lower opening whereby the main package bag body can be opened at either one side of an upper end or a lower end for filling a liquid material to be packaged.