An inspecting device of a display panel includes a contact including first probe pins that contact to data pads of a display panel and second probe pins that contact to common voltage pads of the display panel, a signal generator coupled to the first probe pins, the signal generator configured to generate a first data voltage corresponding to a first gray level and a second data voltage corresponding to a second gray level, a power generator coupled to the second probe pins, the power generator configured to generate a first common voltage and a second common voltage of which a voltage level is different from a voltage level of the second common voltage, and a defect detector configured to detect a defect of the display panel by removing a contact noise generated due to contact failure of the first probe pins and the second probe pins.