A control device on a power receiving side in a contactless power transmission system including a power transmitting device and a power receiving device, the control device comprising: a charging unit configured to charge a battery based on power received by a power receiving unit that receives power from the power transmitting device; a discharging unit configured to perform an operation of discharging the battery and supply the power from the battery to a power supply target; and a control unit configured to control the discharging unit, wherein the control unit configured to start the discharging operation of the discharging unit after an output voltage of the power receiving unit has decreased and a start-up period of the discharging operation has elapsed, wherein further the control unit is configured to start the discharging operation of the discharging unit after the start-up period has elapsed after the output voltage of the power receiving unit decreased below a judgement voltage, the control unit is configured to start discharging of a capacitor, which is charged when the power receiving unit is receiving power, when the output voltage of the power receiving unit has decreased below the judgement voltage, and configured to start the discharging operation of the discharging unit when a charge voltage of the capacitor has decreased below a threshold voltage, and the control unit includes: a first transistor for charging the capacitor; and a second transistor for discharging the capacitor, a control signal that is at a first voltage level when the output voltage of the power receiving unit is greater than or equal to the judgement voltage and at a second voltage level when the output voltage is less than the judgement voltage is input to the control unit, when the control signal is at the first voltage level, the second transistor is turned off, and the first transistor is turned on, and as a result, the capacitor is charged, and when the control signal is at the second voltage level, the first transistor is turned off, and the second transistor is turned on, and as a result, the capacitor is discharged. a charging unit configured to charge a battery based on power received by a power receiving unit that receives power from the power transmitting device; a discharging unit configured to perform an operation of discharging the battery and supply the power from the battery to a power supply target; and a control unit configured to control the discharging unit, wherein the control unit configured to start the discharging operation of the discharging unit after an output voltage of the power receiving unit has decreased and a start-up period of the discharging operation has elapsed, wherein further the control unit is configured to start the discharging operation of the discharging unit after the start-up period has elapsed after the output voltage of the power receiving unit decreased below a judgement voltage, the control unit is configured to start discharging of a capacitor, which is charged when the power receiving unit is receiving power, when the output voltage of the power receiving unit has decreased below the judgement voltage, and configured to start the discharging operation of the discharging unit when a charge voltage of the capacitor has decreased below a threshold voltage, and the control unit includes: a first transistor for charging the capacitor; and a second transistor for discharging the capacitor, a control signal that is at a first voltage level when the output voltage of the power receiving unit is greater than or equal to the judgement voltage and at a second voltage level when the output voltage is less than the judgement voltage is input to the control unit, when the control signal is at the first voltage level, the second transistor is turned off, and the first transistor is turned on, and as a result, the capacitor is charged, and when the control signal is at the second voltage level, the first transistor is turned off, and the second transistor is turned on, and as a result, the capacitor is discharged. a first transistor for charging the capacitor; and a second transistor for discharging the capacitor, a control signal that is at a first voltage level when the output voltage of the power receiving unit is greater than or equal to the judgement voltage and at a second voltage level when the output voltage is less than the judgement voltage is input to the control unit, when the control signal is at the first voltage level, the second transistor is turned off, and the first transistor is turned on, and as a result, the capacitor is charged, and when the control signal is at the second voltage level, the first transistor is turned off, and the second transistor is turned on, and as a result, the capacitor is discharged.