A method of manufacturing a liquid container, the liquid container including a liquid containing chamber in which a liquid can be contained, an air communicating passage allowing the liquid containing chamber to communicate with the air, a liquid supply port for supplying the liquid contained in the liquid container to an outside, a liquid flow passage allowing the liquid container and the liquid supply port to communicate with each other, a valve accommodating chamber disposed in the liquid flow passage, a differential pressure valve which is disposed in the valve accommodating chamber, which is normally urged to a closed state, and which is changed from the closed state to an opened state when a differential pressure of a side of the liquid supply port and a side of the liquid containing chamber is equal to or more than a predetermined value, and a film member forming a part of the valve accommodating chamber, the method includes: pressing a valve body of the differential pressure valve in a direction in which the differential pressure valve is opened; and injecting the liquid from the liquid supply port to the liquid containing chamber via the liquid flow passage while maintaining the opened state of the differential pressure valve.