A power-saving device and method are applicable to a first electronic device having at least one connection interface, and the first electronic device is coupled to a second electronic device via a bus. The power-saving device includes a detection circuit, a power control circuit, and a connection control circuit. The detection circuit is coupled to the connection interface, to detect a load state of the connection interface and generate a detection signal. The power control circuit controls power supplied to the first electronic device via the bus in response to a state of the detection signal. The connection control circuit controls a connection state of the bus according to the detection signal.