Patent ID: 7765652

Claim:
A buckle device comprising: a tongue plate that is part of a seat belt; a buckle main body for which the tongue plate attaches thereto and detaches therefrom; and a switch for monitoring whether the tongue plate is one of attached to and detached from the buckle main body, wherein the buckle main body includes: a frame; an ejector disposed on the frame so as to slide in a direction in which the tongue plate is one of inserted and separated, and which pushes the tongue plate from the buckle main body upon releasing a latched condition between the tongue plate and the buckle main body; and a latch member which rotates to latch the tongue main body upon inserting the tongue plate into the buckle main body, wherein the switch includes: a magnetic detector which outputs a signal corresponding to a magnitude of magnetic flux density; a magnet which applies a magnetic field to the magnetic detector; and a shielding plate which is attached to the ejector and interlocked with the ejector and which changes the magnitude of magnetic flux density provided by the magnet to the magnetic detector in response to a position of the ejector, and wherein the magnetic detector and the magnet are magnetically shielded by at least the frame and the latch member, the frame and the latch member being made of a magnetic material.