A needleless connector comprising: a housing; an inlet and an outlet of a drug solution flow path being respectively provided at one side and another side of a lengthwise direction of the housing; and an elastic valve body having a slit being attached to the inlet of the drug solution flow path of the housing such that the drug solution flow path is switched from a blocked state to a communicating state by opening the slit by the elastic valve body being deformed by means of insertion of a male luer from the inlet of the drug solution flow path, wherein a hollow elastic body is assembled in a state accommodated in an accommodation space of the housing, the hollow elastic body has a tube shape with a bottom equipped with a bottom wall and a peripheral wall such that the hollow elastic body is accommodated and arranged in the accommodation space of the housing in a state opened toward an outlet side of the drug solution flow path so as to form the drug solution flow path between an outer surface of the hollow elastic body and an inner surface of the housing, wherein the hollow elastic body includes a middle protrusion being provided protruding toward an inlet side of the drug solution flow path from a center part of the bottom wall, by means of insertion of a male luer from the inlet side, the bottom wall undergoes elastic deformation so as to enter inside the peripheral wall, and a volume of the drug solution flow path formed between the outer surface of the hollow elastic body and the inner surface of the housing is increased, by means of removal of the male luer, the elastic deformation is cancelled, and the volume of the drug solution flow path is reduced, and a deformation allowance space is provided within the hollow elastic body so that the accommodation space is divided into the inner circumference side deformation allowance space and the outer circumference side drug solution flow path sandwiching the hollow elastic body. a housing; an inlet and an outlet of a drug solution flow path being respectively provided at one side and another side of a lengthwise direction of the housing; and an elastic valve body having a slit being attached to the inlet of the drug solution flow path of the housing such that the drug solution flow path is switched from a blocked state to a communicating state by opening the slit by the elastic valve body being deformed by means of insertion of a male luer from the inlet of the drug solution flow path, wherein a hollow elastic body is assembled in a state accommodated in an accommodation space of the housing, the hollow elastic body has a tube shape with a bottom equipped with a bottom wall and a peripheral wall such that the hollow elastic body is accommodated and arranged in the accommodation space of the housing in a state opened toward an outlet side of the drug solution flow path so as to form the drug solution flow path between an outer surface of the hollow elastic body and an inner surface of the housing, wherein the hollow elastic body includes a middle protrusion being provided protruding toward an inlet side of the drug solution flow path from a center part of the bottom wall, by means of insertion of a male luer from the inlet side, the bottom wall undergoes elastic deformation so as to enter inside the peripheral wall, and a volume of the drug solution flow path formed between the outer surface of the hollow elastic body and the inner surface of the housing is increased, by means of removal of the male luer, the elastic deformation is cancelled, and the volume of the drug solution flow path is reduced, and a deformation allowance space is provided within the hollow elastic body so that the accommodation space is divided into the inner circumference side deformation allowance space and the outer circumference side drug solution flow path sandwiching the hollow elastic body.