A steering wheel includes a boss for fastening the steering wheel to a steering shaft. The airbag includes a left half airbag with a vent hole to be inflated at a front left of a vehicle occupant, and a right half airbag with a vent hole to be inflated at a front right of the vehicle occupant. The position detector also includes a determining unit that determines the presence or absence of the liquid at a position of each of the sound generating elements based on difference in the electrical characteristics measured at the measuring unit. M is one or more transition metal elements.