To provide a locking detection device for a crescent lock or the like, for reliably detecting a locking state while achieving a smaller size and a lower cost by enabling power supply to a detection element by wire from the outside while eliminating the need for power supply to a window body or the like.

A locking detection device 1 is provided for a lock mechanism which can lock a movable body 4 into a closing state with the operation of a lever 25 provided on the movable body 4 capable of opening/closing an opening part. The movable body 4 is provided with a magnet 26 to be moved with the operation of the lever 25, and a pair of yokes 27, 28 extending from a position near the magnet 26 to the end of the movable body 4. Base ends 27a, 28a of the yokes are provided so as to face both magnetic poles of the magnet 26 within a range of the moving track of the magnetic pole of the magnet 26. On a frame body 2 forming the opening part, a magnetic detection element 41 is provided for detecting a magnetic field between front ends 27b, 28b of the yokes.