An injection system using a needleless syringe, comprising: the needleless syringe which injects an injection objective substance into an injection target which is a living body capable of existing in water by emitting the injection objective substance from an emission port without using any injection needle; a transfer passage which is arranged in water and connects a first space which is arranged in water for accommodating a plurality of the injection targets and a second space, which is arranged in water, as a transfer destination of the plurality of injection targets, the transfer passage being installed with the needleless syringe so that the emission port of the needleless syringe is open at inside of the transfer passage; a detecting unit which is capable of detecting transfer through the transfer passage in order for the injection target existing in the first space to go toward the second space; and a control unit which performs emission of the injection objective substance from the emission port of the needleless syringe for every injection target in accordance with the transfer of the injection target, if the transfer of the injection target is detected by the detecting unit and a holding unit which has a holding plate which extends along the transfer passage, and which presses the holding plate against the injection target so that the injection target in the transfer passage is positioned with respect to the needleless syringe, and which temporarily stops the transfer of the injection target in the transfer passage to hold the injection target, and which allows the emission port of the needless syringe to abut against a body surface of the injection target on the basis of a detection result of the transfer of the injection target obtained by the detecting unit. the needleless syringe which injects an injection objective substance into an injection target which is a living body capable of existing in water by emitting the injection objective substance from an emission port without using any injection needle; a transfer passage which is arranged in water and connects a first space which is arranged in water for accommodating a plurality of the injection targets and a second space, which is arranged in water, as a transfer destination of the plurality of injection targets, the transfer passage being installed with the needleless syringe so that the emission port of the needleless syringe is open at inside of the transfer passage; a detecting unit which is capable of detecting transfer through the transfer passage in order for the injection target existing in the first space to go toward the second space; and a control unit which performs emission of the injection objective substance from the emission port of the needleless syringe for every injection target in accordance with the transfer of the injection target, if the transfer of the injection target is detected by the detecting unit and a holding unit which has a holding plate which extends along the transfer passage, and which presses the holding plate against the injection target so that the injection target in the transfer passage is positioned with respect to the needleless syringe, and which temporarily stops the transfer of the injection target in the transfer passage to hold the injection target, and which allows the emission port of the needless syringe to abut against a body surface of the injection target on the basis of a detection result of the transfer of the injection target obtained by the detecting unit.