When a drug solution or the like is administered to a patient, a drug solution that is different from the principal drug solution may be coinjected into a liquid feed passage for drug solution supply, or a liquid flowing through the above-described liquid feed passage may be sampled. In such cases, conventionally, a plug made of rubber is provided in the liquid feed passage as a coinjection port, and the plug is pierced with an injection needle or the like to coinject the drug solution or to collect the liquid.
However, there has been a problem in that if a region of the plug other than a predetermined region to be pierced is pierced with the needle, liquid leakage from that position may occur. In addition, there has been a problem of contamination of the needle due to, for example, a mistake in operation. Recently, a medical port whereby an inserting body whose tip is not sharp can be inserted and held in an insertion hole formed in a valve has been proposed. Patent Document 1 discloses, as an example of a medical port such as this, a medical port having a valve that is adapted so that when, for example, a luer (an inserting body) constituting a syringe tip is pushed into an insertion hole, a liquid can be injected and/or collected, and when the luer is withdrawn from the insertion hole, the insertion hole closes due to its elasticity (see Patent Document 1, for example).