An operational instrument for a fluid injector using a multi-microneedle device, comprising: an outer cylinder having one end opening, another end opening, and a fluid injector housing space extending between the one end opening and the other end opening, the fluid injector housing space holding the fluid injector using the multi-microneedle device movable along a longitudinal axis of the fluid injector; and a selective transfer mechanism provided at the outer cylinder and moving the fluid injector between an initial position, a first protrusion position and a second protrusion position in the fluid injector housing space of the outer cylinder sequentially, a plurality of microneedles of the multi-microneedle device being retracted from the one end opening of the outer cylinder inside the fluid injector housing space at the initial position, the plurality of microneedles of the multi-microneedle device being externally protruded out to a first distance from the one end opening of the outer cylinder at the first protrusion position, the plurality of microneedles of the multi-microneedle device being externally protruded out to a second distance from the one end opening of the outer cylinder at the second protrusion position, the second distance being shorter than the first distance, wherein, at the second protrusion position, fluid can be discharged from the fluid injector through the plurality of microneedles of the multi-microneedle device, characterized in that the operational instrument further comprises: an operational member provided movable relative to an outer periphery surface of the outer cylinder; and a following mechanism that follows the operation of the operational member, the following mechanism moving the fluid injector between the initial position, the first protrusion position and the second protrusion position in the fluid injector housing space of the outer cylinder sequentially, depending on the operation of the operational member. an outer cylinder having one end opening, another end opening, and a fluid injector housing space extending between the one end opening and the other end opening, the fluid injector housing space holding the fluid injector using the multi-microneedle device movable along a longitudinal axis of the fluid injector; and a selective transfer mechanism provided at the outer cylinder and moving the fluid injector between an initial position, a first protrusion position and a second protrusion position in the fluid injector housing space of the outer cylinder sequentially, a plurality of microneedles of the multi-microneedle device being retracted from the one end opening of the outer cylinder inside the fluid injector housing space at the initial position, the plurality of microneedles of the multi-microneedle device being externally protruded out to a first distance from the one end opening of the outer cylinder at the first protrusion position, the plurality of microneedles of the multi-microneedle device being externally protruded out to a second distance from the one end opening of the outer cylinder at the second protrusion position, the second distance being shorter than the first distance, wherein, at the second protrusion position, fluid can be discharged from the fluid injector through the plurality of microneedles of the multi-microneedle device, characterized in that the operational instrument further comprises: an operational member provided movable relative to an outer periphery surface of the outer cylinder; and a following mechanism that follows the operation of the operational member, the following mechanism moving the fluid injector between the initial position, the first protrusion position and the second protrusion position in the fluid injector housing space of the outer cylinder sequentially, depending on the operation of the operational member. an operational member provided movable relative to an outer periphery surface of the outer cylinder; and a following mechanism that follows the operation of the operational member, the following mechanism moving the fluid injector between the initial position, the first protrusion position and the second protrusion position in the fluid injector housing space of the outer cylinder sequentially, depending on the operation of the operational member.