A needleless injector configured to inject an injection intended substance to an injection target region without using an injection needle, by injecting the injection intended substance in a state where the injection target region is pressed, the needleless injector comprising: a containing portion that is provided in a housing of the needleless injector, and is configured to contain the injection intended substance; a drive unit that is provided in the housing, and is configured to generate injection energy for injecting the injection intended substance contained in the containing portion; a nozzle portion that is provided to protrude from a predetermined end portion as a predetermined end portion of the housing on a side of the containing portion, has an injection port formed for injecting toward the injection target region, the injection intended substance provided with the injection energy generated by the drive unit, and is configured to have a distal end portion coming into contact with the injection target region when the injection intended substance is injected from the injection port; and a pressing portion that is provided to protrude from the predetermined end portion and to have a cylindrical shape to surround the nozzle portion with a predetermined gap formed between the nozzle portion and the pressing portion, and is configured to have a distal end portion coming into contact with the injection target region when the injection intended substance is injected from the injection port and a part of the injection target region is received in the predetermined gap when the pressing portion presses the injection target region, wherein the nozzle portion is formed to have a portion of the distal end portion that comes into contact with the injection target region and characterised in that the nozzle portion has a width (a) falling within a range from 3.5 mm to 5.5 mm and a ratio (b/a) defined by an inner diameter (b) of a portion of the distal end portion of the pressing portion that comes into contact with the injection target region by the width (a) of the portion of the distal end portion of the nozzle portion that comes into contact with the injection target region falls within a range from 1.5 to 5.0. a containing portion that is provided in a housing of the needleless injector, and is configured to contain the injection intended substance; a drive unit that is provided in the housing, and is configured to generate injection energy for injecting the injection intended substance contained in the containing portion; a nozzle portion that is provided to protrude from a predetermined end portion as a predetermined end portion of the housing on a side of the containing portion, has an injection port formed for injecting toward the injection target region, the injection intended substance provided with the injection energy generated by the drive unit, and is configured to have a distal end portion coming into contact with the injection target region when the injection intended substance is injected from the injection port; and a pressing portion that is provided to protrude from the predetermined end portion and to have a cylindrical shape to surround the nozzle portion with a predetermined gap formed between the nozzle portion and the pressing portion, and is configured to have a distal end portion coming into contact with the injection target region when the injection intended substance is injected from the injection port and a part of the injection target region is received in the predetermined gap when the pressing portion presses the injection target region, wherein the nozzle portion is formed to have a portion of the distal end portion that comes into contact with the injection target region and characterised in that the nozzle portion has a width (a) falling within a range from 3.5 mm to 5.5 mm and a ratio (b/a) defined by an inner diameter (b) of a portion of the distal end portion of the pressing portion that comes into contact with the injection target region by the width (a) of the portion of the distal end portion of the nozzle portion that comes into contact with the injection target region falls within a range from 1.5 to 5.0.