To provide an applicator that can achieve a further reduction in size and weight. An applicator A1 includes a casing 10, a piston plate 20, a microneedle array 30, a conical coil spring 40, and a release member 50. The casing 10 includes: a tubular main body part 12 that houses therein the piston plate 20 and the conical coil spring 40; and a cover part 14, the cover part 14 and the piston plate 20 sandwiching the conical coil spring 40 therebetween. The main body part 12 includes interior inner walls 12b 1 to 12b 4 that lock the piston plate 20 with the casing 10 by means of projections 20c 1 to 20c 4 . The main body part 12 includes groove parts G1 to G4 that extend in the top-bottom direction. The piston plate 20 is guided in the axial direction of the main body part 12 by the groove parts G1 to G4. If a locked state of the piston plate 20 is released by the release member 50, the piston plate 20 is moved, by the biasing force of the conical coil spring 40, along the groove parts Gl to G4 inside of the main body part 12 to reach a position for action on a skin.