The invention discloses a circuit testing apparatus for testing a device under test. The circuit testing apparatus includes a filtering circuit, an amplifying circuit, a comparing module, and a result-examining module. The filtering circuit filters an analog output signal generated from the device under test to generate a filtered signal. The amplifying circuit amplifies the filtered signal to generate an amplified signal. The comparing module compares the amplified signal with at least one reference level to generate at least one result signal accordingly. The result-examining module examines the result signal to determine a test result for the device under test.