To provide an armature being manufactured with high efficiency and reducing friction against fluid.

This armature accommodated in a motor casing filled with liquid is provided with a laminated core in which a plurality of magnetic plates 17 are laminated. Each of the magnetic plates 17 includes: an outermost circumferential edge 17d extending along an arc with a certain radius around the center; and recessed portions recessed inside from the outermost circumferential edge 17d at a plurality of portions in the circumferential direction of the outermost circumferential edge 17d. When observed from the laminating direction, the plurality of magnetic plates 17 are laminated with a positional relationship in which the recessed portions are aligned in the same circumferential position and the radius of the outermost circumferential edge 17d changes in a period of an integral multiple of thicknesses in the magnetic plates 17 along a direction in parallel with the center line.