PURPOSE: To certainly prevent the fixing of the seal part of a slide plug by preventing the inclination of a slide plug 13 when said plug moves slowly by providing a guide part to the slide plug.

CONSTITUTION: A slide plug 13 formed from an elastic material such as silicone rubber is received in a main ink chamber 16 in a freely slidable manner. The slide plug 13 is equipped with a columnar main body 31 and an annular seal part 32 is integrally provided to the outer periphery of the upper end part of said main body 31 in a protruding state and lightly brought into contact with the inner peripheral surface of the main ink chamber 16 to keep sealability. A plurality of, for example, four guide parts 33 are integrally provided to the outer periphery of the lower end part of said main body 31 in a protruding state and slightly brought into contact with the inner peripheral surface of the main ink chamber 16 or slightly spaced apart therefrom to prevent the tilting of the slide plug 13 with respect to the axial line of the main ink chamber 16.