To securely auto-lock a pair of right and left side swing doors by one lock device (hook lock).

A lock body 14 comprises a casing 15 mountable on one of the swing doors 5, a latch 17 swingably installed in the casing 15 and having a hook part 16 disappearably installed in the casing 15, a drive member 18 laterally movably stored in the casing 15 so as to be moved to a receiving member 14 side by a magnetic force when these both swing doors 4 and 5 are closed, an energizing member 19 energizing the hook part 16 of the latch 17 to a recessing side, an interlocking mechanism 20 projecting and recessing the latch 17 from and into the casing 15 in association with the lateral movement of the drive member 18, and an operation member 21 for unlocking operation to return the latch 17 in a projected state into a recessed state.