the present invention aims at offering : a syringe connectable to a port in a fixed manner as well as capable of demonstrating high operational performance even in the case of direct connection where a connector is not used ; a connector used for the syringe ; and a syringe able to attach the connector thereto . for the attainment of the above objectives , the medical syringe of the present invention is a medical syringe including a cylindrical connection supporting member which enhances the holding force of a luer part inserted into a port when the medical syringe is connected to the port . the connection supporting member is set by sliding along the luer or a syringe body in a state of being movable between a first position near a tip of the luer and a second position away from the tip of the luer . the medical syringe is characterized in that , when the connection supporting member is moved to the second position , the tip of the luer part is exposed .