A testing device including a first connector, a control unit, a first detecting circuit and a memory controller is provided. The first connector is electrically connected to a first bus. The control unit generates a plurality of first control signals according to a first enable signal from the first connector. The first detecting circuit is electrically connected to a plurality of first transmission lines in the first bus, and sequentially conducts the first transmission lines to a ground according to the first control signals. The memory controller detects states of the signals transmitted by the first transmission lines and determines whether to generate a first abnormal indication signal according to a detecting result. The control unit controls a plurality of indication lights according to the first abnormal indication signal.