An ultraviolet irradiation device includes: a light source which irradiates ultraviolet curable ink with ultraviolet rays; and a jetting port which jets gas to form a gas film facing the light source in an irradiation direction. A secondary packing chamber or gland is installed on an existing valve to intercept leakage past the valve’s original primary packing gland, which otherwise would escape past the valve stem to the atmosphere. The particles are configured to provide an electrode porosity that militates against excess water accumulation in the electrode formed from the ink composition upon a drying thereof. At least one of the head portion and the screw nut includes a convex surface which is oriented towards the respective flange, and the respective flange includes, at the mounting hole, a flange recess which is oriented towards the convex surface.