An antenna level display device capable of faithfully reflecting any deterioration of a picture quality in receiving a satellite broadcast. In this display device, orthogonal detection of an input signal is executed in a demodulator, and a CN ratio is calculated from a conversion table in a ROM according to the mean value of deflections of mapped points of the received signal on an IQ plane. The demodulated data is compared, in a comparator, with the demodulated data obtained after error correction by a Viterbi decoder, and a CN ratio is calculated on the basis of the bit error rate from a conversion table stored in another ROM. A decision is made to select one CN ratio, which is to be displayed as an antenna level, out of the two calculated CN ratios, and the selected CN ratio is displayed through adaptive switching. Consequently, despite any deterioration of the receiving environment derived from occurrence of phase noise in a converter or the like, it is still possible to display a proper antenna level reflecting the receiving circumstances.