An improved hair dryer includes a fan unit and a heating unit to generate a linear heated air current which can mix with outside cold air to obtain a rotational air current of moderate temperature and to increase the capability of penetrating a user's hair. Therefore, the air provided by the hair dryer would not become both hot and dry, but maintain an ideal, moderate temperature suitable for users, so that users may feel more comfortable while dressing their hairs. Furthermore, the increased capability of penetrating a user's hair allows the hair to be dried more quickly.