To prevent faint writing or writing failure from occurring during a writing operation due to back shock and to reduce shock sound by using a simple structure, a pressure contact member protrudes from one surface or both surfaces on the side of a shaft tube and a knock body so as to come into sliding contact with each other, parts on the side of the shaft tube and the knock body being opposed to each other in a radial direction. Accordingly, even when the part on the side of the knock body retreats with respect to the part on the side of the shaft tube in terms of a releasing operation, a retreat speed of an ink tank becomes slow due to a friction resistance of the pressure contact member, and thus back shock remarkably reduces. As a result, ink does not flow to the ink tank in a reverse direction due to air introduced from a writing tip portion, and shock sound generated when the retreating ink tank returns to a normal position reduces.