A ballpoint pen including: an ink accommodation cylinder; a ballpoint pen tip in which a ball is rotatably held, the pen tip being attached to a tip end of an ink-accommodation cylinder directly or through a tip holder; and ballpoint oil-based ink comprising at least a coloring agent, organic solvent, a lubricant comprising organic acid and phosphoric ester, and organic amine, the ink having ink viscosity at shearing speed 6.8 sec.sup.-1 of 500 to 6000 mPas (20.degree. C.) and directly being accommodated in the ink-accommodation cylinder, wherein the ballpoint pen satisfies 2.5.times.10.sup.-3.gtoreq.Z.gtoreq.1.0.times.10.sup.-3 where ink amount per 1 mm.sup.2 is Z mg/mm.sup.2 which is calculated from Y=X.times.10.sup.5.times.Z where writing width of the ballpoint pen is X mm and ink consumption per 100 m is Y mg.