The present invention relates to a device at a bone cement mixer, wherein the bone cement mixer (1) comprises at least one mixing space (5) for mixing powder and liquid components (2, 4), preferably a polymer and a monomer respectively, to make bone cement, the powder component (2) is placed in the mixing space (5) and the liquid component (4) in a liquid container (3), and the liquid component (4) is sucked out from the liquid container (3) to the mixing space (5) and the powder component (2) placed therein by means of vacuum generated in said mixing space. According to the invention, the liquid container (3) is a tube (15) or bag of such metal material which prevents the liquid component (4) from escaping from it, has the tube (15) or bag a connecting element (16) for connecting it to the bone cement mixer (1), is the tube (15) or bag closed and adapted to being opened when it is connected to a corresponding connecting element (17) on the bone cement mixer (1), so that the liquid component (4) is sucked out from the tube or bag into the mixing space (5) by means of said vacuum therein, and is the tube (15). or bag designed and the metal material of the tube or bag has a thickness such that the volume of its liquid containing space (18) is brought to decrease when said vacuum in the mixing space (5) is brought to prevail also therein when the liquid component is sucked out therefrom.