To provide a vent cap capable of securing a sufficient ventilating amount even coming into contact with a waterproof sheet wound around a ventilation tube part.

This vent cap 19 is fitted to the ventilation tube 12 having, at its upper end, a ventilation hole 13 for a drain pipe W. The waterproof sheet 8 installed on the upper surface 2a of a penthouse 1 is continuously wound on the outer periphery of the tube 12 so as to be raised upward. The cap 19 comprises an upper cover 21 and a sheet cover 22. The upper cover 21 secures the ventilation of the ventilation port 13 and covers the upper part of the ventilation port 13. The sheet cover 22 is formed integrally with the upper cover 21, an upper end 22d is positioned at the generally same height as the lower end 21a of the upper cover, and covers the wound portion 8a of the sheet 8 on the ventilation tube 12. The cap 19 comprises a recessed part 22b for ventilation for forming a ventilation passage R enabling ventilation to be secured when the sheet 8 is brought into contact with the lower end 22a of the sheet cover.