Ink for ballpoint pens and ballpoint pen using same

A ballpoint pen ink containing at least a colorant, a liquid medium in which 50% by weight or more of the liquid medium is an organic solvent, polyoxyethylene castor oil, polyoxyethylene hardened castor oil or a derivative thereof represented by the following formula (I), and one kind of a compound or a mixture of two or more kinds of compounds selected from any of the compounds represented by the following formulae (II), (III) and (IV):

• (X:
• an ethylene oxide group, CH2CH2O,
• Y:
• H, CR or COCH2CH2COOH,
• R:
• a fatty acid or hydroxyl group-containing fatty acid having C12 or more,
• α+β+γ=an integer of 1 or more,
• δ+ε+ξ=an integer of 1 or more), more, and
• α+β+γ+δ+ε+ξ<80);
• (R:
• an alkyl group or a phenyl group, and
• α:
• an integer of 0 or more);
• (R:
• an alkyl group or a phenyl group, and
• α+β=an integer of 0 or more);
• and
• (R:
• an alkyl group or a phenyl group, and
• α+β+γ=an integer of 0 or more).