PURPOSE: To make a decision whether an AC adapter can be used or not without operating a device by measuring no-load output voltage of an AC adapter and an output voltage of the AC adapter when a test load is connected and then determining a power supply capacity.

CONSTITUTION: A load switch control means 25 turns load connecting switches 28, 29 and a power switch 5 OFF and a voltage detecting means 20 detects no-load voltage of an AC adapter 1. A measurement result decision means 21 then processes 22 no-load voltage measurement results and if a no-load voltage does not conform to the regulations for devices A, B, the fact is notified to a display processing means 30. When the adapter 1 can be used, a connecting means 25 sequentially changes over switches 28, 29 and the detecting means 20 measures respective load voltages. The decision means 21 then processes 23 load voltage measurement results and when the adapter 1 can be used, a power switch control means 26 turns the switch 5 ON to connect the adapter 1 with the device A or B.