To provide a lock device capable of locking a window firmly.

In this lock device, a connection screw 20d is removed, and connection of a connection plate 19 and a first lock cam 16 by use of the connection screw 20d is released to lock the window by a key. When the key is inserted into a key hole in a cylinder lock 13 and is turned in the direction of unlocking, the first lock cam 16 is turned by a cylinder cam 15, and a second lock cam 17 is turned to release the engagement with a second window part 18b. A first engaging lock part 16b raises a slider 18. When the key is turned in the opposite direction, the cylinder cam 15 is inverted, and the first lock cam 16 is turned to lower the slider 18. A second lock cam 17 turns and returns by the moment action due to self-weight, the first engaging lock part 16b is engaged with a first window part 18a of the slider 18, and a second engaging lock part 17b is engaged with the second window part 18b of the slider 18 to lock the rise of the slider 18 in a double manner.