Abstract: The cap for writing equipment comprises an air vent in the top portion, means installed on the inner peripheral surface for providing airtightness, a miniature cap movably enclosed in the axial direction in a space formed with the top face, the inner peripheral face and an annular boss for providing airtightness, a resilient seal positioned on the outside of the top of the miniature cap for blocking the ventilation between the air vent and the inside of the cap when the tip of the pen body is fitted into the cap and rebounders for pressing the miniature cap against the pen body. The annular boss for providing airtightness is so positioned as to block the ventilation in the longitudinal direction by forcing itself to contact the trunk of the pen when the tip of the pen body is fitted into the cap.