PROBLEM TO BE SOLVED: To provide a nozzle exchange type medicine injector capable of smoothly performing an attachment/detachment operation of a nozzle attachment, and yet, preventing loosening of the nozzle attachment caused by oil breeding.SOLUTION: A nozzle exchange type medicine injector 1 comprises a syringe 2 provided with a nozzle part 4 and a luer lock part 5 at a tip, and a nozzle attachment 3 exchangeably screwed at the tip of the syringe 2. The nozzle exchange type medicine injector further comprises: a first engagement part 13 provided around the outer periphery of the luer lock part 5 and a second engagement part 16 that, when the nozzle attachment 3 is threadedly advanced to a lock position, is engaged with the first engagement part 13 in the circumferential direction so as to inhibit reverse rotation of the nozzle attachment 3 with respect to the luer lock part 5.
