An opening device of a liquid food container includes a bottom, a main body, and a top part joined to an upper end of the main body and formed with thermoplastic resin. The top part has a lid integrally moulded with thermoplastic resin. The lid divides the top part and includes weakening lines, a first lid part, a second lid part, and a gripper. A first hinge is formed between the first lid part and the second lid part, the weakening lines are cut when the gripper is pulled up, and the-first lid part rotates on the-first hinge such that the weakening lines open narrowly. A second hinge is formed in an edge of the second lid part, the weakening lines are cut by further pulling the gripper, and the second lid part rotates on the second hinge such that the weakening lines open more widely.