To provide a synthetic resin-made capsule body with a compact structure capable of fitting a cup to a container for beverage in the sanitary state thereof stored in a capsule.

The synthetic resin-made capsule body 1 comprises a bottomed cylindrical capsule body 5 having, on the outside of a bottom part 8, a fitting part 7 for detachably fitting and fixing the capsule body to an end part 4a of the container 4 for beverage, a capsule cover 6 detachably installed on the capsule body to close an opening part of the capsule body 5, and a cup 3 having a bottom part fixed to the inner surface of a top wall 12 of the capsule cover 6. When the capsule cover 5 is removed from the capsule body 6 and the cup 3 is extended, the cup 3 is brought into a usable state. After the cup is used, the cup 3 is retracted to store it in the capsule body 1.