PURPOSE: To efficiently and accurately test a large number of batteries to be tested by preventing the momentary breaks of electric currents by using diodes which prevents the reverse flow of electric currents.

CONSTITUTION: At the time of disconnecting fully charged batteries A3-N4 to be tested from a test circuit 19 during the course of charging characteristic tests, switches S21.8-S2N14 are turned off and diodes D11.11-D1N17 for preventing reverse flow of electric currents are turned on. Then the batteries A3-N4 are by-passed so that they do not short-circuit by turning on switches S41.10-S4N16. After the batteries A3-N4 are by-passed, the batteries A3-N4 are cut off from a charging circuit by turning off switches S11.7-S1N13. Thereafter, the disconnecting operations of the batteries A3-N4 from the testing circuit 19 are completed by turning on the switches S21.8-S2N14 and by-passing the diodes D11.11-D1N17. At the time of connecting the batteries A3-N4 to the circuit 19, the above-mentioned operation are performed reversely. Therefore, the momentary break of the charge and discharge currents can be prevented at the time of connecting and disconnecting the batteries A3-N4 to and from the circuit 19.