Provided is an operational instrument by which a desired amount of a fluid can be readily and reliably injected into skin tissue in a brief period of time in instances of intradermal injection with a fluid injector using a multi-microneedle device. This operational instrument (14) is provided with: an outer cylinder (16) which extends between one end opening (16a) and another end opening (16b) and has a housing space (16c) for retaining an injector (12) so as to enable movement along the longitudinal axis thereof and a mechanism (18) for sequentially moving the injector within the accommodation space between an initial position where a plurality of microneedles (10c) of a main body (10b) of a needle device are retracted into the one end opening, a first protrusion position where the microneedles are externally protruded out to a first distance from the one opening, and a second protrusion position where the microneedles are externally protruded out to a second distance shorter than the first distance from the one opening. A fluid is discharged from the injector at the second protrusion position via the needles of the needle device.
