A writing instrument has an ink reservoir (22) under pressure. Compressed ink in the ink reservoir (22) is supplied through an ink passage (27) to a ball tip (24) also acting as a valve body. A push rod (32) is inserted in the ink passage (27) and is intended to urge the ball (26) forward. The ball tip (24) is in a closed state when the writing instrument is used and is in an open state when the writing instrument is used for supplying ink. A stirring weight (31) is housed in the ink reservoir (22). When the writing instrument is swung, the stirring weight (31) is moved to stir ink in the ink reservoir (22). The stirring weight (31) interferes with the push rod (32) to displace it. The push rod (32) is displaced to stir ink in the ink passage (27) whereby ink containing air and/or air bubbles in the ink passage (27) is removed.