A current output circuit comprising: a DC-DC power source configured to receive power from a power source and control an output voltage; a current output unit configured to operate at the output voltage of the DC-DC power source, to generate a current signal based on a control instruction that includes information related to a measurement result of a measurement apparatus, and to output the current signal to a load; and a voltage detector configured to hold a voltage of the load at a peak thereof and output the voltage of the load held at the peak to the DC-DC power source as a voltage signal; wherein: the voltage detector comprises an input unit connected to the DC-DC power source and an output unit configured to hold the voltage signal at the peak; the input unit comprises a switching element connected between the DC-DC power source and the output unit; the output unit includes a capacitor and a resistor; the switching element of the input unit is configured to turn on when the voltage of the load is equal to or higher than the voltage held by the output unit and the capacitor in the output unit is configured to be charged through the switching element by applied voltage from the DC-DC power source; the switching element of the input unit is configured to turn off when the voltage of the load is lower than the voltage held by the output unit and the capacitor in the output unit is configured to be discharged to the resistor in the output unit; the output unit is configured to output the voltage of the capacitor as the voltage signal to the DC-DC power source; and the DC-DC power source is configured to output the output voltage as a sum of the voltage signal and an offset voltage that secures a margin, the margin enabling the output voltage to follow fluctuations in the voltage of the load. a DC-DC power source configured to receive power from a power source and control an output voltage; a current output unit configured to operate at the output voltage of the DC-DC power source, to generate a current signal based on a control instruction that includes information related to a measurement result of a measurement apparatus, and to output the current signal to a load; and a voltage detector configured to hold a voltage of the load at a peak thereof and output the voltage of the load held at the peak to the DC-DC power source as a voltage signal; wherein: the voltage detector comprises an input unit connected to the DC-DC power source and an output unit configured to hold the voltage signal at the peak; the input unit comprises a switching element connected between the DC-DC power source and the output unit; the output unit includes a capacitor and a resistor; the switching element of the input unit is configured to turn on when the voltage of the load is equal to or higher than the voltage held by the output unit and the capacitor in the output unit is configured to be charged through the switching element by applied voltage from the DC-DC power source; the switching element of the input unit is configured to turn off when the voltage of the load is lower than the voltage held by the output unit and the capacitor in the output unit is configured to be discharged to the resistor in the output unit; the output unit is configured to output the voltage of the capacitor as the voltage signal to the DC-DC power source; and the DC-DC power source is configured to output the output voltage as a sum of the voltage signal and an offset voltage that secures a margin, the margin enabling the output voltage to follow fluctuations in the voltage of the load. the voltage detector comprises an input unit connected to the DC-DC power source and an output unit configured to hold the voltage signal at the peak; the input unit comprises a switching element connected between the DC-DC power source and the output unit; the output unit includes a capacitor and a resistor; the switching element of the input unit is configured to turn on when the voltage of the load is equal to or higher than the voltage held by the output unit and the capacitor in the output unit is configured to be charged through the switching element by applied voltage from the DC-DC power source; the switching element of the input unit is configured to turn off when the voltage of the load is lower than the voltage held by the output unit and the capacitor in the output unit is configured to be discharged to the resistor in the output unit; the output unit is configured to output the voltage of the capacitor as the voltage signal to the DC-DC power source; and the DC-DC power source is configured to output the output voltage as a sum of the voltage signal and an offset voltage that secures a margin, the margin enabling the output voltage to follow fluctuations in the voltage of the load.