A printing mechanism 6 of a screen printing machine 1 for printing paste P at a printing position to a work W through a screen S includes a packing nozzle 62 coming into contact, at the distal end thereof, with the screen, a packing head 62 to which the paste consumed during printing is packed and a feed tank 63 for supplying the paste to the filling head. Each of the packing head and the feed tank has therein an extrusion mechanism 62b, 63a and can control an extrusion pressure of the paste to the screen. The printing mechanism further includes a packing head supporting mechanism 64 capable of supporting the packing head in such a manner as to be capable of moving up and down and also capable of regulating the pushing force of the packing head onto the screen.