A needleless injector that injects a substance to be injected to a target region without using an injection needle, the needleless injector comprising: an encapsulating portion configured to encapsulate the substance to be injected; a pressurizing portion configured to pressurize the substance to be injected encapsulated in the encapsulating portion ; and a flow path including an ejection port through which the substance to be injected pressurized by the pressurizing portion is ejected to the target region, wherein the pressurizing portion pressurizes the substance to be injected having an ejection pressure defined as a pressure of the substance to be injected ejected through the ejection port , the ejection pressure being raised to a first peak pressure (P1) after pressurizing is started, being lowered to a pressure lower than the first peak pressure afterward, and then being raised to a second peak pressure (P2) again, and an on-completion reached depth (Df) that is an on-completion reached depth of the substance to be injected in the target region when the pressurizing portion completes pressurizing is adjustable, the on-completion reached depth (Df) being increased along with increase of the first peak pressure (P1) and being increased along with reduction of a length between peaks from a first timing (T1) at which the ejection pressure reaches the first peak pressure (P1) to a second timing (T2) at which the ejection pressure reaches the second peak pressure (P2); the needless injector further comprising: an igniter including an ignition charge; and a gas generating agent that is disposed in a combustion chamber into which a combustion product generated by combustion of the ignition charge flows and that is combusted by the combustion product and generates predetermined gas, wherein the pressurizing portion causes the ejection pressure of the substance to be injected to reach the first peak pressure (P1) with a combustion pressure of the ignition charge by operating the igniter , and causes the ejection pressure of the substance to be injected to reach the second peak pressure (P2) with a combustion pressure of the gas generating agent that is combusted subsequent to the ignition charge. an encapsulating portion configured to encapsulate the substance to be injected; a pressurizing portion configured to pressurize the substance to be injected encapsulated in the encapsulating portion ; and a flow path including an ejection port through which the substance to be injected pressurized by the pressurizing portion is ejected to the target region, wherein the pressurizing portion pressurizes the substance to be injected having an ejection pressure defined as a pressure of the substance to be injected ejected through the ejection port , the ejection pressure being raised to a first peak pressure (P1) after pressurizing is started, being lowered to a pressure lower than the first peak pressure afterward, and then being raised to a second peak pressure (P2) again, and an on-completion reached depth (Df) that is an on-completion reached depth of the substance to be injected in the target region when the pressurizing portion completes pressurizing is adjustable, the on-completion reached depth (Df) being increased along with increase of the first peak pressure (P1) and being increased along with reduction of a length between peaks from a first timing (T1) at which the ejection pressure reaches the first peak pressure (P1) to a second timing (T2) at which the ejection pressure reaches the second peak pressure (P2); an igniter including an ignition charge; and a gas generating agent that is disposed in a combustion chamber into which a combustion product generated by combustion of the ignition charge flows and that is combusted by the combustion product and generates predetermined gas, <EOS>