An injector for injecting an injection objective substance into an injection target region, the injector comprising: an injector main body having a through-hole formed in an axial direction; a piston section arranged so as to be slidable inside the through-hole ; a syringe section arranged on a tip side of the injector main body , the syringe section having a storage chamber which is capable of storing the injection objective substance, a plunger which pressurizes the injection objective substance inside the storage chamber as the piston section slides, and a nozzle section which includes a flow path through which the injection objective substance that is present inside the storage chamber and has been pressurized by the plunger flows and which ejects the injection objective substance from an ejection port formed at a tip of the flow path; an ignition device having a partition member which forms a first space to store a gunpowder and which is formed by a prescribed rigid material such that the partition member is breached due to a rise in pressure of the first space when the gunpowder is burned; and a case of which a base section is fixed on a side of the ignition device and which is arranged in a space inside the injector main body so as to cover the ignition device , the case defining a second space with the partition member of the ignition device and encapsulating, inside the second space , a combustion product generated by combustion of the gunpowder in the ignition device , characterised in that the case includes: an extending section which, due to a rise in pressure inside the second space by gunpowder combustion in the ignition device , extends in an approach direction in which a part of the case approaches a prescribed end section of the piston on a side opposite to an end section opposing the plunger ; and a pressing section which is provided in the part of the case and which presses the prescribed end section of the piston as the extending section extends. an injector main body having a through-hole formed in an axial direction; a piston section arranged so as to be slidable inside the through-hole ; a syringe section arranged on a tip side of the injector main body , the syringe section having a storage chamber which is capable of storing the injection objective substance, a plunger which pressurizes the injection objective substance inside the storage chamber as the piston section slides, and a nozzle section which includes a flow path through which the injection objective substance that is present inside the storage chamber and has been pressurized by the plunger flows and which ejects the injection objective substance from an ejection port formed at a tip of the flow path; an ignition device having a partition member which forms a first space to store a gunpowder and which is formed by a prescribed rigid material such that the partition member is breached due to a rise in pressure of the first space when the gunpowder is burned; and a case of which a base section is fixed on a side of the ignition device and which is arranged in a space inside the injector main body so as to cover the ignition device , the case defining a second space with the partition member of the ignition device and encapsulating, inside the second space , a combustion product generated by combustion of the gunpowder in the ignition device , an extending section which, due to a rise in pressure inside the second space by gunpowder combustion in the ignition device , extends in an approach direction in which a part of the case approaches a prescribed end section of the piston on a side opposite to an end section opposing the plunger ; and a pressing section which is provided in the part of the case and which presses the prescribed end section of the piston as the extending section extends. <EOS>