Abstract: A buckling device for a vehicle seat belt comprises a locking portion arranged within a buckle so as to lock a tongue plate, a lock controlling mechanism to selectively hold said locking in a locked position where it is engageable with said tongue plate and in an unlocked position where it is unengageable with said tongue plate, and an actuating unit to dislodge the locking condition between said tongue plate and said locking portion. With the structure as stated, the lock controlling mechanism is adapted to move said locking portion from the unlocked position to the locked position associated with the inserting operation of said tongue plate into said buckle, while return said locking portion to the original unlocked position associated with the unlocking operation by unit of said actuating means.