PURPOSE: To accurately measure loose contact inferiority by successively supplying a large current pulse and a random pulse to a semiconductor device to be tested as a test signal and comparing a test result signal with said test signal.

CONSTITUTION: A screening pulse current PS larger than the max. rated current P2 of a transistor 1 to be tested and the rated current P2 are successively applied to the base and emitter of the transistor 1 to be tested from a current pulse generating part 2IP. Next, a pulse group PR random in pulse width is applied thereto from a random pulse generating part 2RP. A comparison circuit 3 compares a test signal VT with the number of pulses or pulse width of the pulse VR outputted from the transistor 1 and, when both of them do not coincide, the transistor 1 to be tested is judged to be inferior because of the presence of loose contact.