For improving horn switch operability, an air bag apparatus 4 supports the side wall 26b of the cover body 26 and is movable back and forth on the outer periphery of the surrounding wall 24 of the base plate 24. Hook 24h protrudes from the surrounding wall 24b and is locked onto lock receiving portion 26h of the side wall 26b, thereby regulating the moving range of the cover body 26. Bracket 35 is mounted on the under surface of the covering portion 26a and is positioned at each of the spokes 7. A movable first contact 36e, 136e is mounted on the bracket 35. A fixed contact support portion 31 is provided on the outer peripheral surface of the side wall 24b of the base plate 24 to protrude therefrom or support 131 in the shape of a pillar is provided integrally to protrude from the core metal 7a of the spoke 7. A fixed second contact 31d, 131d that is opposed to the movable contact 36e, 136e is provided to oppose the movable contact 36e, 136e.