To solve the following problem: when infants and small children who can drink a beverage only from a nursing bottle in a growing process are to drink various kinds of beverages in PET bottles, content in the PET bottle has to be transferred to the nursing bottle.

By using a connecting instrument 4 and connecting a nipple part 1 of a nursing bottle on the market and a mouth of a PET bottle 8, an infant can easily drink a beverage inside the PET bottle. However an air pressure inside the PET bottle needs to be adjusted when an infant or a little child sucks the content, and the connecting instrument 4 is provided with an airway 5 for air pressure adjustment in order to solve the problem. Also, the connecting instrument 4 is provided with a flange 7 for facilitating attachment and detachment mutually among the three of the connecting instrument 4, a lid part 3 of the nursing bottle and the PET bottle 8. By carrying the lid part 3 of a usually used nursing bottle and the connecting instrument 4, the beverage in the PET bottle on the market can be drunk directly.