The invention discloses a circuit testing apparatus for testing a device under test. The circuit testing apparatus includes a precision measurement unit, a signal transformation module, and a microprocessor. The precision measurement unit is coupled to the device under test for providing a testing signal and receiving a measurement signal generated according to the testing signal. The signal transformation module is coupled to the precision measurement unit for receiving the measurement signal and transforming the measurement signal to a signal measurement result according to a predetermined manner. The microprocessor is coupled to the precision measurement unit and the signal transformation module for examining the signal measurement result to determine a test result for the device under test.