An instrument for manipulating a fluid injector that uses a multi-microneedle device, that is, a manipulation instrument (14, 14') for a fluid injector that uses a multi-microneedle device, characterized in that the instrument comprises: an outer cylinder (16, 16') that has a one-end opening and an other-end opening, and a fluid injector housing space that extends between the one-end opening and the other-end opening and movably holds the fluid injector that uses the multi-microneedle device, along a longitudinal center line of the fluid injector; and a selective movement mechanism configured to move the fluid injector between a first jutting position and a second jutting position in the fluid injector housing space of the outer cylinder, the first jutting position allowing a plurality of microneedles of the multi-microneedle device to jut out into an external space by a first distance from the one-end opening of the outer cylinder, the second jutting position allowing the plurality of microneedles of the multi-microneedle device to jut out into the external space by a second distance that is shorter than the first distance from the one-end opening of the outer cylinder, wherein: the fluid injector is configured to discharge a fluid at the second jutting position via the plurality of microneedles of the multi-microneedle device; and the selective movement mechanism includes a rotational-linear movement conversion mechanism that is interposed between the outer cylinder (16, 16') and the fluid injector, and that is configured to move the fluid injector between the first jutting position and the second jutting position along a longitudinal center line of the outer cylinder, in conformity with a direction and amount of rotation of the outer cylinder relative to the fluid injector, wherein the rotational-linear movement conversion mechanism includes an internal threaded portion provided to an inner surface of a peripheral wall of the outer cylinder (16, 16'), and an external threaded portion provided to the fluid injector to threadably engage with the internal threaded portion of the outer cylinder. an outer cylinder (16, 16') that has a one-end opening and an other-end opening, and a fluid injector housing space that extends between the one-end opening and the other-end opening and movably holds the fluid injector that uses the multi-microneedle device, along a longitudinal center line of the fluid injector; and a selective movement mechanism configured to move the fluid injector between a first jutting position and a second jutting position in the fluid injector housing space of the outer cylinder, the first jutting position allowing a plurality of microneedles of the multi-microneedle device to jut out into an external space by a first distance from the one-end opening of the outer cylinder, the second jutting position allowing the plurality of microneedles of the multi-microneedle device to jut out into the external space by a second distance that is shorter than the first distance from the one-end opening of the outer cylinder, wherein: the fluid injector is configured to discharge a fluid at the second jutting position via the plurality of microneedles of the multi-microneedle device; and the selective movement mechanism includes a rotational-linear movement conversion mechanism that is interposed between the outer cylinder (16, 16') and the fluid injector, and that is configured to move the fluid injector between the first jutting position and the second jutting position along a longitudinal center line of the outer cylinder, in conformity with a direction and amount of rotation of the outer cylinder relative to the fluid injector, wherein the rotational-linear movement conversion mechanism includes an internal threaded portion provided to an inner surface of a peripheral wall of the outer cylinder (16, 16'), and an external threaded portion provided to the fluid injector to threadably engage with the internal threaded portion of the outer cylinder. the fluid injector is configured to discharge a fluid at the second jutting position via the plurality of microneedles of the multi-microneedle device; and the selective movement mechanism includes a rotational-linear movement conversion mechanism that is interposed between the outer cylinder (16, 16') and the fluid injector, and that is configured to move the fluid injector between the first jutting position and the second jutting position along a longitudinal center line of the outer cylinder, in conformity with a direction and amount of rotation of the outer cylinder relative to the fluid injector, wherein the rotational-linear movement conversion mechanism includes an internal threaded portion provided to an inner surface of a peripheral wall of the outer cylinder (16, 16'), and an external threaded portion provided to the fluid injector to threadably engage with the internal threaded portion of the outer cylinder.