Uninterruptible power supply device, and uninterruptible power supply system using same

This uninterruptible power supply device (U1) is provided with: a converter (40); an inverter (41); a bidirectional chopper (24); and a control device (53). The bidirectional chopper (24) includes: first to fourth transistors (Q11-Q14); first to fourth diodes (D11-D14); and first and second coils (51, 52). During a charging mode, the control device (53) alternately turns on the first and fourth transistors (Q11, Q14), and controls the on time of each of the first and fourth transistors (Q11, Q14) such that the detection values of first and second currents (I1, I2) flowing through the first and second coils (51, 52) correspond.