An operation tool includes a mechanism sequentially moving the injector in a space of an outer cylinder among an initial position in which needles of a main body of the device are retracted inside the space, a first position in which the needles protrude to the outside by a first distance, and a second position in which needles protrude to the outside by a second distance shorter than the first distance. Fluid flows from the injector through the needles in the second position. The mechanism has a unit forcing the injector toward the initial position by a magnetic force, first and second stoppers which can be selectively extended/retracted with respect to the outer peripheral wall of the outer cylinder, and an engaging portion which is selectively engaged with these stoppers on the outer peripheral wall of the injector and selectively arranging the injector in the above three positions.