In a controlling circuit, a photo coupler is used for isolating noises, and a general purpose amplifier is used for adjusting a gain, so that a logic tester may test analog signals in cooperation with relays having different specifications and operating voltage level differences in an analog measurement module. A shift register of each controlling circuit of a controlling module also transmits a test data signal to a next stage controlling circuit, so that a logic tester may simultaneously output a plurality of bits to multiple controlling circuits and multiple analog measurement modules by using merely one I/O port.