PURPOSE: To prevent the mixing of air bubbles from a nozzle during conveyance and the dripping of ink, by a method wherein a shear type valve is connected to the discharge part part of a three-port valve which is, in turn, opened during the operation of a printing apparatus while closed when the printing apparatus is conveyed.

CONSTITUTION: In a charge amount control type ink jet printing apparatus having a three-port valve 1, a shear type valve is connected to the discharge port part EXH of the three-port valve 1 which is, in turn, brought to a closed state when the printing apparatus is conveyed while brought to a opened state when the printing apparatus is stationary. It is pref. to form such a structure that, when the printing apparatus is held under stationary state on a desk, a weight 19 is on the desk and, therefore, a stopper 18, a yoke 16 and the shear valve 11 are positioned as shown by a solid line to open the valve while the weight 19 is fallen when the printing apparatus is lifted to close the valve.