An electronic apparatus with a detection function includes a normal function circuit, a dummy function circuit and a processing module. The normal function circuit operates according to an operation signal. The dummy function circuit operates to generate a result signal according to a test signal and is a small size circuit of the normal function circuit. The test signal and operation signal are same function signals, and the test signal has an electrical characteristic larger than that of the operation signal. The processing module generates the operation signal and the test signal at the same time, accumulates an operation time of the dummy function circuit, and determines whether the dummy function circuit is faulty by detecting the result signal. When the dummy function circuit is faulty, the processing module calculates a remaining lifetime of the normal function circuit according to the test signal, the operation signal and the operation time.