Abstract: A power on ready (POR) signal generating apparatus and an operation method thereof are provided. The POR signal generating device includes a detection circuit and a control circuit. The detection circuit detects a target voltage. When the target voltage is ready, the detection circuit sets a POR signal to a ready state. The control circuit is coupled to the output terminal of the detection circuit to receive the POR signal. After the POR signal transitions from a not ready state to the ready state, the control circuit maintains the POR signal in the ready state, and the control circuit disables the detection circuit.