A housing of an electric motor is fitted with an oil seal having the function of sealing an output shaft (rotary shaft) of the motor. The housing is provided with a hole for motor airtightness testing communicating with an internal space of the motor. A local or annular projection configured to close the hole for motor airtightness testing, thereby maintaining the airtightness of the internal space of the electric motor, is disposed on that surface of the oil seal which faces the housing.