A medicine discharge stopper for a medical bag of a type where a multiple of medicines are mixed, aiming to positively exclude a possibility of generation of erroneous operation that administration is done without opening the mixing seal. The medical bag is formed from a soft film and has an inner space, which is divided into compartments 20 and 22. An outlet port 12 is provided so that it is opened to the first compartment 20. The stopper includes split halves, which, when tied, form an inner space 34 of the outlet port 12. The combination is done under a resilient force by cantilever fashioned extending parts 38. When the weak seal portion is opened, an impact-like hydraulic force is generated and the bag is widened, which causes the flaps 30 and 32 to be opened against the resilient force, resulting in a release of the stopper. The flaps 30 and 32 are made separable from the body parts, which allows the stopper to be also utilized for a holder of needle during the execution of infusion process.
