A power supply system comprising: a switching power supply configured to convert an input voltage applied from a main power supply and output the converted voltage; and a control device to be supplied with power from the switching power supply, wherein the switching power supply includes: a transformer; a semiconductor switching element that is connected to a primary coil of the transformer; a switch control unit that is configured to control the switching of the semiconductor switching element; and a rectifying/smoothing circuit that is provided on a secondary side of the transformer, wherein the switch control unit is to be supplied with power from the main power supply, configured to start to control the switching of the semiconductor switching element, and configured to oscillate a primary side of the transformer to induce a voltage on the secondary side of the transformer, the control device is configured to, during an output mode in which the switching power supply smoothes the voltage induced on the secondary side and outputs the smoothed voltage, output a control pulse signal to the switch control unit to stop the oscillation of the transformer, thereby changing the output mode of the switching power supply to an output stop mode, wherein the control device includes a first electric storage unit that is charged by the output of the switching power supply and serves as a power supply for the control device in the output stop mode, wherein the switch control unit includes: a driver circuit that is configured to output an on/off signal to the semiconductor switching element to oscillate the transformer; a start circuit that is to be supplied with power from the main power supply and starts; a first power circuit that is configured to start with the start of the start circuit and to supply power to the driver circuit in the output mode; an oscillation stop circuit that is configured to break the first power circuit to stop the oscillation of the transformer when the control pulse signal is input in the output mode; a restart circuit that is configured to restart the start circuit when the control pulse signal is input in the output stop mode; and a second power circuit (69, 73) that is configured to supply power to the restart circuit in the output stop mode. a switching power supply configured to convert an input voltage applied from a main power supply and output the converted voltage; and a control device to be supplied with power from the switching power supply, wherein the switching power supply includes: a transformer; a semiconductor switching element that is connected to a primary coil of the transformer; a switch control unit that is configured to control the switching of the semiconductor switching element; and a rectifying/smoothing circuit that is provided on a secondary side of the transformer, wherein a transformer; a semiconductor switching element that is connected to a primary coil of the transformer; a switch control unit that is configured to control the switching of the semiconductor switching element; and a rectifying/smoothing circuit that is provided on a secondary side of the transformer, wherein the switch control unit is to be supplied with power from the main power supply, configured to start to control the switching of the semiconductor switching element, and configured to oscillate a primary side of the transformer to induce a voltage on the secondary side of the transformer, the control device is configured to, during an output mode in which the switching power supply smoothes the voltage induced on the secondary side and outputs the smoothed voltage, output a control pulse signal to the switch control unit to stop the oscillation of the transformer, thereby changing the output mode of the switching power supply to an output stop mode, wherein the control device includes a first electric storage unit that is charged by the output of the switching power supply and serves as a power supply for the control device in the output stop mode, wherein the switch control unit includes: a driver circuit that is configured to output an on/off signal to the semiconductor switching element to oscillate the transformer; a start circuit that is to be supplied with power from the main power supply and starts; a first power circuit that is configured to start with the start of the start circuit and to supply power to the driver circuit in the output mode; an oscillation stop circuit that is configured to break the first power circuit to stop the oscillation of the transformer when the control pulse signal is input in the output mode; a restart circuit that is configured to restart the start circuit when the control pulse signal is input in the output stop mode; and a second power circuit (69, 73) that is configured to supply power to the restart circuit in the output stop mode. a driver circuit that is configured to output an on/off signal to the semiconductor switching element to oscillate the transformer; a start circuit that is to be supplied with power from the main power supply and starts; a first power circuit that is configured to start with the start of the start circuit and to supply power to the driver circuit in the output mode; an oscillation stop circuit that is configured to break the first power circuit to stop the oscillation of the transformer when the control pulse signal is input in the output mode; a restart circuit that is configured to restart the start circuit when the control pulse signal is input in the output stop mode; and a second power circuit (69, 73) that is configured to supply power to the restart circuit in the output stop mode.