A signal generating circuit for detecting ground status includes a power supply input unit (A), a step down rectified power supply or DC power supply unit (C) in series. The DC power supply required by a signal detection and process unit (D) is obtained by the power supply input unit (A) passing through the step down DC power supply unit (C), and then a ground status signal is obtained and outputted via a resistor unit (B) and the signal detection and process unit (D) connected in turn.