An automatic contact ink stamping apparatus for printing predetermined indicia particularly adapted for marking assembly lines parts or other objects which is characterized by a dual acting piston stroke assembly which is operatively attached to a stamp platen to move the platen between an inking position adjacent to an ink supply and a stamping position adjacent to the work piece. The stamp platen is mounted to a horizontal slide assembly which includes an opening having a pair of inclined walls. A vertically extending stem connected to the stamp platen is provided with bearing surfaces which cooperate with the inclined walls of the slide assembly and a cooperating carriage member to transfer a terminal portion of the horizontal stroke length of the piston into vertical displacement of the stamp platen at the respective ink supply and ink stamping stations.