Provided are: a needleless syringe whereby an immune response can be selectively induced and a method for introducing DNA containing a region said region encoding an antigen capable of causing selective production of an antibody into the body of a mammal using the needleless syringe. The needleless syringe for injecting a DNA solution into an injection target area without using an injection needle comprises: a housing part for housing a DNA solution a definite ignition device and a nozzle part through which the DNA solution said DNA solution being pressurized by the combustion of a definite ignition charge in the ignition device flows and which is provided with a jetting port for jetting the DNA solution toward the injection target area. In the needleless syringe during the pressurization of the DNA solution for jetting the temperature of a definite combustion product at the pressurization shifts to the vicinity of ordinary temperature within 20 msec after the pressure which is applied to the DNA solution by the combustion of the ignition charge attains a first peak jetting force.
