A mixing machine adapted to mix a liquid mixture containing bitumen with solid granules so as to obtain a homogenised bituminous mix. The machine comprising a cylindrical container arranged coaxially to a vertical axis and capable of containing the liquid mixture containing bitumen and the solid granules, a heating circuit for heating the inner side surface of the cylindrical container, a mixing assembly mounted axially rotatable within the container to rotate about the vertical axis, and a driving unit adapted to rotate the mixing assembly about the vertical axis. The mixing assembly comprises a helicoidal blade which extends coaxial to the axis within the container and has its outer peripheral edge in contact with the inner surface of the container so as to scrape the material adhering on the inner surface during its rotation.