The electric motor is the electric motor that includes a shaft part that rotates around a rotation shaft and a casing that accommodates at least part of the shaft part. A through hole is formed in the casing at a position that overlaps with the rotation shaft. A set screw is screwed into the through hole so as to close the through hole. An O-ring is interposed between the casing and the set screw so as to suppress intrusion of water and dust into the casing.