To securely hold an opening/closing element closed in an earthquake, etc.

This lock device comprises a main body part 8 having a cylinder part 8a inserted into a through hole in a door 2 from the inside of the door 2; a cover 9 provided in such a way as to cover the main body part 8; a claw member 10 provided in such a way as to freely move up and down inside a space formed by the main body part 8 and the cover 9, and having at its lower end a tapered claw part 10a that projects from an opening in the lower end of the cover 9; and a spring 11 that activates the claw part 10a of the claw member 10 in a direction in which it projects from the opening in the lower end of the cover 9. The lock device also includes a cam member 12 which, in order to press the claw member 10 into the space against the force of the spring 11, abuts to the tapered surface 10c of the claw part 10a and turns about a position near the middle of the height of the claw member 10; an external thread member 14 whose head is locked to the lower end of the cam member 12 and projects from the door 2 through the cylinder part 8a; and a handle 15 fitted over the end of the male thread member 14 projecting from the door 2.