A voltage detection device provided for a battery pack (51, 51a) which includes a series circuit having two or more battery blocks (BT1-BT4, BT11-BT14) connected in series and generates a desired voltage across both ends of the series circuit, the voltage detection device for detecting output voltage of each of the battery blocks (BT1-BT4, BT11-BT14), each of the battery blocks (BT1-BT4, BT11-BT14) including one or more unit cells (BT1-BT4), the voltage detection device comprising: a voltage selector which is connected to positive electrode terminals of the battery blocks (BT1-BT4, BT11-BT14) through connection lines (L1-L4, L11-L14) and selects output voltage of each of the battery blocks (BT1-BT4, BT11-BT14) based on the voltages generated at the positive electrode terminals; the voltage detection device is characterised by: first switches (15; SW11-SW14) provided between the positive electrode terminals and the connection lines (L1-L4, L11-L14), respectively; an A/D converter for digitizing a signal of the output voltage selected by the voltage selector; a reference voltage output unit (N1-N4) capable of supplying different levels of reference voltages to the respective connection lines (L1-L4, L11-L14); a second switch (SW21, SW22) for switching between supply and cutoff of the reference voltages outputted from the reference voltage output unit (N1-N4) to the respective connection lines (L1-L4, L11-L14); a controller performing a control to turn on the first switches (15; SW11-SW14) and turn off the second switch (SW21, SW22) in a process of detecting the output voltages of the battery blocks (BT1-BT4, BT11-BT14) and to turn off the first switches (15; SW11-SW14) and turn on the second switch (SW21, SW22) in a process of fault diagnosis for the voltage selector and the A/D converter; and a fault detector which determines based on a voltage signal outputted from the A/D converter whether at least one of the voltage selector and A/D converter is failing in the process of fault diagnosis. a voltage selector which is connected to positive electrode terminals of the battery blocks (BT1-BT4, BT11-BT14) through connection lines (L1-L4, L11-L14) and selects output voltage of each of the battery blocks (BT1-BT4, BT11-BT14) based on the voltages generated at the positive electrode terminals; the voltage detection device is characterised by: first switches (15; SW11-SW14) provided between the positive electrode terminals and the connection lines (L1-L4, L11-L14), respectively; an A/D converter for digitizing a signal of the output voltage selected by the voltage selector; a reference voltage output unit (N1-N4) capable of supplying different levels of reference voltages to the respective connection lines (L1-L4, L11-L14); a second switch (SW21, SW22) for switching between supply and cutoff of the reference voltages outputted from the reference voltage output unit (N1-N4) to the respective connection lines (L1-L4, L11-L14); a controller performing a control to turn on the first switches (15; SW11-SW14) and turn off the second switch (SW21, SW22) in a process of detecting the output voltages of the battery blocks (BT1-BT4, BT11-BT14) and to turn off the first switches (15; SW11-SW14) and turn on the second switch (SW21, SW22) in a process of fault diagnosis for the voltage selector and the A/D converter; and a fault detector which determines based on a voltage signal outputted from the A/D converter whether at least one of the voltage selector and A/D converter is failing in the process of fault diagnosis. first switches (15; SW11-SW14) provided between the positive electrode terminals and the connection lines (L1-L4, L11-L14), respectively; an A/D converter for digitizing a signal of the output voltage selected by the voltage selector; a reference voltage output unit (N1-N4) capable of supplying different levels of reference voltages to the respective connection lines (L1-L4, L11-L14); a second switch (SW21, SW22) for switching between supply and cutoff of the reference voltages outputted from the reference voltage output unit (N1-N4) to the respective connection lines (L1-L4, L11-L14); a controller performing a control to turn on the first switches (15; SW11-SW14) and turn off the second switch (SW21, SW22) in a process of detecting the output voltages of the battery blocks (BT1-BT4, BT11-BT14) and to turn off the first switches (15; SW11-SW14) and turn on the second switch (SW21, SW22) in a process of fault diagnosis for the voltage selector and the A/D converter; and a fault detector which determines based on a voltage signal outputted from the A/D converter whether at least one of the voltage selector and A/D converter is failing in the process of fault diagnosis.