A printing unit particularly intended for price labelling machines, comprising annular printing wheels supporting matrices at their outer periphery and equidistantly spaced notches at their inner periphery into which notches engages a rod to advance the wheels to forward the desired matrix to printing position. The printing pressure is obtained by an impact rod striking a shoulder formed on a pressure arm, the movement of which is transferred to the associated printing wheel forcing the intended matrix thereon against the place of printing. As the printing wheel is stationary during the printing operation the resulting print is sharp and clear.