A container for addition (co-infusion) of medicine to an infusion bag and aims to keep a positive sealed condition while preventing a number of parts from being increased and while maintaining a positive releasing of the sealed condition when an infusion process is carried out. A breakable lug 20 is integrally formed at a end of a port body 10 to which a soft container 80 for storing therein with a co-infusion liquid under a sealed manner, which lug 20 is able to be broken in order to obtain a release function. A rubber plug 98 of an infusion bag 90 is pierced by a needle body 11, while the port body 10 is press fitted into a straight bore of the needle body 11, so that the lug 20 is contacted with an opposed bottom wall of the needle body 11, resulting in at least partial breakage of the lug 20, thereby forming an opening 89 at the portion where the breakage is taken place, so that the medicine in the soft container 80 is transported (co-infused) into the infusion bag 90.
