A cap includes a main unit 11 fit onto the mouth of a double-walled container, a spout cylinder 12 provided on the main unit, an inner stopper 15 that is provided in the main unit 11, and a first inner valve 31. The inner stopper 15 includes a communicating part 29 that communicates with the inside of the inner container and the inside of the spout cylinder 12. The first inner valve 31 includes a first valve body 33 that covers the communicating part. The first valve body 33 has passage holes 35. The first valve body 33 being deformed from a closing position S toward an opening position O keeps acting as a partition between the communicating part 29 and the spout cylinder 12.