PURPOSE: To adjust effective capacity for filling in a container by producing the container for filling a tablet or the like provided initially with a seal.

CONSTITUTION: This is a container unit comprising a casing 20 and a container member 1 integrally formed with a closure 10 including a lid 11 sealed initially with an original seal 12. A separate bottom piece 30 for a container is permanently secured to the casing of the container member with a product preferably by rotation-friction welding, and both the bottom part and the casing are made of polypropylene. The container member is filled through the opening edge end 21 of the casing with the closure facing downward. Then the bottom part is inserted in the open edge end of the container casing, and is rotation friction welded to the casing. A partition 36 is inserted in the casing to define a space for a product corresponding to the volume of the product.