Abstract: A seat belt buckle, in which a locking member is mounted in a channel-shaped base member and a tongue can be inserted between the base member and locking member and locked in engagement with a tongue engaging surface of the locking member, comprising first and second symmetrical guide holes formed in said base member, a slider movably disposed in the base member, a first guide member being movable in said first guide holes and urging said locking member, a second guide member penetrating said second guide holes and movable together with said slider through said second guide holes, a tensile coil spring coupling together said first and second guide members, and a button member for releasing said first guide member from its locking state.