A digital demodulating apparatus comprises a tuner constituted by circuit elements to perform channel select processing to a signal; a demodulator that performs demodulation processing to a signal output from the tuner; a power supply unit that supplies a normal power to each circuit element, and supplies to the circuit element a test power different from the normal power, over a first time period in place of the normal power; a test noise measuring unit that measures the intensity of test noise contained in a signal to be output from the tuner, when the power supply unit supplies the test power over the first time period; a comparing unit that compares the intensity of the test noise measured by the test noise measuring unit with a noise reference value as a reference for updating of the normal power; and a power updating unit that updates the intensity of the normal power on the basis of a result of the comparison by the comparing unit.