To provide a device for preventing construction machine thefts capable of preventing construction machines from being stolen even in the case that another person except a normal operator acquires an engine key.

The console 5 of an operator cab is provided with a starting switch 3 to start the engine, a code input device 15 to input a lock code, a code judging part to judge whether the lock code inputted from the code input device 15 is a predetermined one or not, and an activating means 8 to expose the keyway 3a of the starting switch 3 according to the result of judgement of the code judging part. Thereby, since the starting switch 3 is rotated by the drive of the motor 19 of the activating means 8 to expose the keyway 3a from the opening 5a of the console 5 in the case that the lock code inputted via the code input device 15 is a predetermined one, it is possible to start the engine by an engine key 29. On the other hand, since the motor 19 is not driven to maintain the keyway 3a in an unexposed initial state in the case that the inputted lock code is not a predetermined one, it is possible to prevent the starting of the engine.