Disclosed is a handle locking device including a first frame, a first hook and a second frame, wherein a second hook is provided on the first frame. The first and second hooks are rotatably installed on the first frame, and the second frame capable of fixing the first hook and the first frame. Since the handle locking device is only be installable on a circuit breaker by mating between the first hook and a first installation part of the circuit breaker and mating between the second hook and a second installation part of the circuit breaker, an operator is prevented from unintentionally setting an “OFF” position of the handle locking device in an “ON” position of the circuit breaker during installation. The first hook is rotatably installed on the first frame, so that the handle locking device can be conveniently and rapidly installed on or demounted from the circuit breaker.