A syringe for injecting an injection objective substance into an injection target area of a living body without using any injection needle, the syringe comprising: an enclosing unit which encloses the injection objective substance; an ignition device including an ignition charge that exhibits such a characteristic that a plasma having a high temperature and a high pressure is generated during a combustion immediately after the ignition, but a generated pressure is suddenly lowered because of no gas component to be contained when an ordinary temperature is given and a combustion product is condensed; a combustion chamber into which the combustion product produced by combustion of the ignition charge is allowed to flow and which accommodated a gas generating agent that is to be combusted by the combustion product to produce a predetermined gas; a pressurizing unit which pressurizes the injection objective substance enclosed in the enclosing unit; and a flow passage unit which defines a flow passage so that the injection objective substance, which is pressurized by the pressurizing unit, is allowed to inject to the injection target area, wherein the pressurizing unit has: a first pressurizing mode in which a pressure applied to the injection objective substance in the pressurizing unit is raised to a first peak pressure (P1max) in order to allow the injection objective substance to penetrate through a surface of the injection target area, and then the pressure applied to the injection objective substance is lowered to a waiting pressure (Pw); and a second pressurizing mode in which the injection objective substance having the waiting pressure (Pw) is pressurized so that the pressure applied to the injection objective substance is raised to a second peak pressure (P2max) to inject a predetermined injection amount of the injection objective substance, characterized in that the pressurizing unit uses an increase in pressure generated by the combustion of the ignition charge in the ignition device as a pressurization transition until arrival at the first peak pressure (P1max) in the first pressurizing mode, and an increase in pressure brought about by the predetermined gas produced by the gas generating agent as a pressurization transition until arrival at the second peak pressure (P2max) in the second pressurizing mode. an enclosing unit which encloses the injection objective substance; an ignition device including an ignition charge that exhibits such a characteristic that a plasma having a high temperature and a high pressure is generated during a combustion immediately after the ignition, but a generated pressure is suddenly lowered because of no gas component to be contained when an ordinary temperature is given and a combustion product is condensed; a combustion chamber into which the combustion product produced by combustion of the ignition charge is allowed to flow and which accommodated a gas generating agent that is to be combusted by the combustion product to produce a predetermined gas; a pressurizing unit which pressurizes the injection objective substance enclosed in the enclosing unit; and a flow passage unit which defines a flow passage so that the injection objective substance, which is pressurized by the pressurizing unit, is allowed to inject to the injection target area, wherein the pressurizing unit has: a first pressurizing mode in which a pressure applied to the injection objective substance in the pressurizing unit is raised to a first peak pressure (P1max) in order to allow the injection objective substance to penetrate through a surface of the injection target area, and then the pressure applied to the injection objective substance is lowered to a waiting pressure (Pw); and a second pressurizing mode in which the injection objective substance having the waiting pressure (Pw) is pressurized so that the pressure applied to the injection objective substance is raised to a second peak pressure (P2max) to inject a predetermined injection amount of the injection objective substance, a first pressurizing mode in which a pressure applied to the injection objective substance in the pressurizing unit is raised to a first peak pressure (P1max) in order to allow the injection objective substance to penetrate through a surface of the injection target area, and then the pressure applied to the injection objective substance is lowered to a waiting pressure (Pw); and a second pressurizing mode in which the injection objective substance having the waiting pressure (Pw) is pressurized so that the pressure applied to the injection objective substance is raised to a second peak pressure (P2max) to inject a predetermined injection amount of the injection objective substance, characterized in that the pressurizing unit uses an increase in pressure generated by the combustion of the ignition charge in the ignition device as a pressurization transition until arrival at the first peak pressure (P1max) in the first pressurizing mode, and an increase in pressure brought about by the predetermined gas produced by the gas generating agent as a pressurization transition until arrival at the second peak pressure (P2max) in the second pressurizing mode.