A liquid injection method for a liquid container for an ink jet recording, the container including a flexible liquid containing portion for containing liquid in substantially hermetically sealed state, a casing, having an inside configuration equivalent or similar to an outer configuration of the liquid containing portion, for separably covering the liquid containing portion, a liquid discharging portion for permitting the liquid to be discharged to outside, the method includes supplying the liquid having a temperature higher than a normal temperature into the liquid containing portion; substantially hermetically sealing the liquid discharging portion with a liquid discharge permission member for permitting the liquid to discharge in use.