A vehicle power supply control circuit , comprising: a first input terminal (T1) to which a voltage output from an DC-DC converter configured to convert a power supply voltage is supplied; a second input terminal (T2) to which the power supply voltage (VT2) is supplied; an output terminal (T3) configured to output a voltage for controlling semiconductor elements (Tr1,...,Tr6) being configured to generate a drive current for a motor generator (G), the semiconductor elements (Tr1,...,Tr6) having unsaturated region characteristics; a switch circuit (Y) having one end connected to the first input terminal (T1) and another end connected to the output terminal (T3), the switch circuit (Y) is configured to turn on based on a signal applied to a control terminal (TC) thereof to establish electrical connection between the first input terminal (T1) and the output terminal (T3), on the other hand, the switch circuit (Y) is configured to turn off based on a signal applied to the control terminal for cutting off between the first input terminal (T1) and the output terminal (T3); and a switch controller (X) configured to control the switch circuit (Y) by applying a signal to the control terminal based on the power supply voltage (VT2) of the second input terminal (T2), wherein the switch controller (X) is configured to turn on the switch circuit (Y), when the power supply voltage (VT2) supplied to the second input terminal (T2) rises and becomes equal to or higher than a preset first threshold voltage while the switch circuit (Y) is off, and after the power supply voltage (VT2) rise higher than a second threshold voltage while the switch circuit (Y) is on, the switch controller (X) is configured to turn off the switch circuit (Y), when the power supply voltage (VT2) supplied to the second input terminal (T2) drops and becomes less than the second threshold voltage different from the first threshold voltage. a first input terminal (T1) to which a voltage output from an DC-DC converter configured to convert a power supply voltage is supplied; a second input terminal (T2) to which the power supply voltage (VT2) is supplied; an output terminal (T3) configured to output a voltage for controlling semiconductor elements (Tr1,...,Tr6) being configured to generate a drive current for a motor generator (G), the semiconductor elements (Tr1,...,Tr6) having unsaturated region characteristics; a switch circuit (Y) having one end connected to the first input terminal (T1) and another end connected to the output terminal (T3), the switch circuit (Y) is configured to turn on based on a signal applied to a control terminal (TC) thereof to establish electrical connection between the first input terminal (T1) and the output terminal (T3), on the other hand, the switch circuit (Y) is configured to turn off based on a signal applied to the control terminal for cutting off between the first input terminal (T1) and the output terminal (T3); and a switch controller (X) configured to control the switch circuit (Y) by applying a signal to the control terminal based on the power supply voltage (VT2) of the second input terminal (T2), wherein the switch controller (X) is configured to turn on the switch circuit (Y), when the power supply voltage (VT2) supplied to the second input terminal (T2) rises and becomes equal to or higher than a preset first threshold voltage while the switch circuit (Y) is off, and after the power supply voltage (VT2) rise higher than a second threshold voltage while the switch circuit (Y) is on, the switch controller (X) is configured to turn off the switch circuit (Y), when the power supply voltage (VT2) supplied to the second input terminal (T2) drops and becomes less than the second threshold voltage different from the first threshold voltage. <EOS>