A buckle device includes a switch having a Hall element which outputs a signal in accordance with a magnitude of a magnetic flux density, a magnet which applies a magnetic field to the Hall element, and a shielding plate which is attached to an ejector so as to change the magnitude of the magnetic flux density transmitted from the magnet to the Hall element in accordance with a position of the ejector. The Hall element and the magnet are magnetically shielded by at least a frame and a latch member which are formed of a magnetic material.