A built-in-self-test apparatus for an analog-to-digital converter includes a digital-to-analog converter, a low-pass filter, a histogram analyzer and a software engine. The digital-to-analog converter is intended to generate a first signal. The low-pass filter is intended to smoothen the first signal so that an analog-to-digital converter can perform sampling on the smoothened first signal by a second signal, wherein the bit number of the second signal is greater than or equal to that of the first signal, and the frequency of the second signal is a multiple of that of the first signal. The histogram analyzer is electrically connected to the output end of the analog-to-digital converter. The software engine is electrically connected to the output end of the histogram analyzer so as to display the characteristics of the analog-to-digital converter.