PROBLEM TO BE SOLVED: To provide a luer connector and a medicament injection device capable of reducing the amount of non-radioactive water injected to a medicament administration target.SOLUTION: A luer connector 10 comprises: a cylindrical male luer 11 with a through hole 11c and a female luer 12 with a male luer fit-in hole 12a which fits with the male luer 11. The female luer 12 comprises a cylindrical spacer 13 which is inserted into the through hole 11c of the male luer 11 at the time of fitting with the male luer 11, the outer peripheral surface 13a of the spacer 13 being tapered.