To provide a method for injecting a beverage, which can easily and surely perform inflow of a content from one container to the other container between containers for beverages including different kinds of the contents.

One container 1 includes: one container body 2 with an opening mouth 2a; and a cap 3 having a first connecting means connected with the mouth of the container body on one end, and a second connecting means connected attachably/detachably to the mouth of the other container on the other end. The cap is provided with a communicating path for communicating the container body with the other container, a partition provided on this communicating path, and a communicating means for opening this partition. The cap is mounted on the mouth of one container through the first connecting means, and under a condition that one container is inverted, the mouth of the container, in which the content is partly consumed, is connected with the second connecting means of the cap, and the partition is opened by the communicating means of the cap, to make the content of one container flow into the other container.