Electrical safety is always an important item of medical equipment in hospital. With the development of clinical engineering, the electric safety testing has become a routine procedure for the unit of clinical engineering in hospital. Among the parameters of safety standard of medical equipment, the leakage currents are more important than others. This study is aimed in the measurement of different leakage currents. An intelligent and digital tester was applied to test the safety quality of medical instrument automatically. This tester was based on a chip-computer (INTER 8031). This tester was designed to be able to set up as normal status or single failure status for automatic test by electric relays. All the results, free from manual errors, are displayed by means of a LCD unit and printed by a micro-printer. The output of high accuracy is also an advantage of this instrument, which is based on a precise signal detection electrical circuit and adaptive filter. This tester can be easily used for the clinic unit follow the standard of China GB9706 as well as IEC standard 601 and UL2601.