A power supply control circuit comprising: a control means that controls an operation of a control target; a power supply unit that supplies power to the control means; a power switch that connects the power supply unit and the control means; a bypass circuit that includes a first semiconductor switch and is capable of bypassing the power switch to maintain connection between the power supply unit and the control means; and a cut-off circuit that includes a second semiconductor switch and is disposed between the bypass circuit and the control means, wherein the cut-off circuit includes a signal supply source that supplies a bypass circuit ON signal for turning on the first semiconductor switch, wherein when the second semiconductor switch is in an off state, a leakage current generated between the control means and the power supply unit via the bypass circuit is cut off by the cut-off circuit, and when the second semiconductor switch is turned on by a switch-on signal output from the control means, the first semiconductor switch is turned on and the bypass circuit bypasses the power switch to maintain connection between the power supply unit and the control means; wherein the bypass circuit includes: an upstream circuit portion that branches from an upstream side of the power switch and is connected to an upstream side of the first semiconductor switch; a downstream circuit portion that is connected from a downstream side of the first semiconductor switch to a circuit portion between the power switch and the power supply unit; and a first input circuit (R1, R2, C2) for inputting the bypass circuit ON signal to the first semiconductor switch connected to a downstream side of the second semiconductor switch in the cut-off circuit, and the cut-off circuit includes: the signal supply source that is connected to an upstream side of the second semiconductor switch; a second input circuit (R4, C1) for inputting the switch-on signal from the control means to the second semiconductor switch; and a branch circuit portion that is branched from the second input circuit (R4, C1) and is connected to a circuit portion between the signal supply source and the second semiconductor switch. a control means that controls an operation of a control target; a power supply unit that supplies power to the control means; a power switch that connects the power supply unit and the control means; a bypass circuit that includes a first semiconductor switch and is capable of bypassing the power switch to maintain connection between the power supply unit and the control means; and a cut-off circuit that includes a second semiconductor switch and is disposed between the bypass circuit and the control means, wherein the cut-off circuit includes a signal supply source that supplies a bypass circuit ON signal for turning on the first semiconductor switch, wherein when the second semiconductor switch is in an off state, a leakage current generated between the control means and the power supply unit via the bypass circuit is cut off by the cut-off circuit, and when the second semiconductor switch is turned on by a switch-on signal output from the control means, the first semiconductor switch is turned on and the bypass circuit bypasses the power switch to maintain connection between the power supply unit and the control means; wherein the bypass circuit includes: an upstream circuit portion that branches from an upstream side of the power switch and is connected to an upstream side of the first semiconductor switch; a downstream circuit portion that is connected from a downstream side of the first semiconductor switch to a circuit portion between the power switch and the power supply unit; and a first input circuit (R1, R2, C2) for inputting the bypass circuit ON signal to the first semiconductor switch connected to a downstream side of the second semiconductor switch in the cut-off circuit, and the cut-off circuit includes: the signal supply source that is connected to an upstream side of the second semiconductor switch; a second input circuit (R4, C1) for inputting the switch-on signal from the control means to the second semiconductor switch; and a branch circuit portion that is branched from the second input circuit (R4, C1) and is connected to a circuit portion between the signal supply source and the second semiconductor switch.