Abstract: The body (1) of the container is provided with a frangible internal diaphragm (4) which sub-divides it into two superimposed chambers (1b, 1c), one containing a beverage and the other containing an additive substance. Above the diaphragm (4), in the body (1) of the container, is mounted a cutting tool (5) having at least one cutting edge (7a) facing the diaphragm (4), which is engageable by a drinking straw (11) in the first stage of the introduction of the straw (11) into the container, and can pierce the diaphragm (4) due to its being driven by the straw (11). The substance in the upper chamber (1b) falls under gravity through the pierced diaphragm (4) into the lower chamber (1c), in which it mixes with the other substance under the action of the cutting tool (5) which rotates due to the axial sliding of a threaded portion (13) of the straw (11) in a nut carried by the body (1) of the container in the zone of introduction of the straw (11).