Provided are an opening device and a liquid food container, wherein a sealing property is superior and a straw hole can be easily opened, and from which the liquid food can be drunk with a straw, can be directly drunk with the mouth, and can be poured. Disclosed is an opening device for a liquid food container provided at the top portion with a lid body which is integrally formed with a thermoplastic resin and covers a pouring port, wherein the lid body is provided with a weakened line which defines the top portion and seals so that the seal can be easily cut, the lid body comprises a first lid portion located on the front face side of the container, a second lid portion located at the rear face side of the container, and a grip portion projecting from the first lid portion, a first hinge is provided between the first lid portion and the second lid portion so that when the grip portion is pulled up, the first lid portion is rotated around the first hinge to have a narrow opening, and a second hinge is provided at the edge on the container rear face side of the second lid body so that when the grip portion is further pulled up, the second lid portion is rotated around the second hinge to have a wider opening.