a rotation shaft;

a permanent magnet disposed at an outer circumference of the rotation shaft, the permanent magnet having a ring shape and including an outer circumference part and an inner circumference part; and

a shaft fixing member configured to fix the permanent magnet and the rotation shaft, the shaft fixing member including a fixing groove,

wherein the permanent magnet further includes:

an end extending in an inner radial direction of the permanent magnet from the outer circumference part,

a taper part extending from the end to be inclined toward an inside of the permanent magnet,

an inner extension extending in the inner radial direction of the permanent magnet from the taper part and connected to the inner circumference part, and

a fixing protrusion that protrudes upward in an axial direction from the inner extension towards the end and is configured to be accommodated in the fixing groove, the fixing protrusion has a predetermined curvature,

wherein the fixing protrusion includes a plurality of fixing protrusions that are provided along a circumferential direction of the inner circumference part of the permanent magnet, one of the plurality of fixing protrusions and another one of the plurality of fixing protrusions being disposed across from each other at opposite sides of the inner circumference part and define a portion of an outer circumference of a same cylinder, and

wherein a first distance from the inner extension to the end is greater than a second distance from the inner extension to an uppermost tip of the fixing protrusion,

wherein a first length of the uppermost tip of the fixing protrusion in the inner radial direction is greater than a second length of the inner extension in the inner radial direction, and

wherein the fixing protrusion includes an innermost surface that extends downward in the axial direction from the uppermost tip of the fixing protrusion and is coplanar with the inner circumference part.