Abstract: A linear spring (12) for urging a writing ball (2) of a ball point pen forward in a longitudinal direction of the pen without fail is simple in construction, and is therefore produced at a low cost. The pen comprising: a ball housing (1) a front end portion of which is caulked to rotatably hold the wiring ball (2) therein; a holder (5) having a front and a rear end portion thereof inserted into the ball housing (1) and an ink reservoir pipe (15), respectively. The rear end portion of the holder (5) is reduced in diameter, and extends rearward to form an ink inlet portion (9) which is provided with an ink inlet opening (10). A rear end opening of this ink inlet portion (9) is closed with a spring support (11). The linear spring (12) is movably received in the holder (5), and has a length slightly longer than a distance between the writing ball (2) and an inner axial end surface of the spring support (11).