T. Zwitter, University of Ljubljana; and U. Munari, Astronomical Observatory, Padova, report the discovery by S. Moretti, on unfiltered CCD images taken on Sept. 27 with a 0.4-m telescope at Ravenna, of a bright supernova (mag 12.8) in NGC 6946. The new object is located at R.A. = 20h35m25s.33, Decl. = +60o07'17".7 (equinox 2000.0). A high-resolution spectrogram, secured on Sept. 28 with the echelle spectrograph at the 1.82-m telescope in Asiago, shows a relatively featureless spectrum with a very broad, low-contrast H_alpha emission. Sharp interstellar Na I absorption lines are observed at heliocentric radial velocities of -21.1 (± 0.7) and +45.2 (± 0.4) km/s, matching expectation for separate origin within our galaxy and NGC 6946. The equivalent width of Na I D_2 lines corresponds to a total reddening of E(B-V) = 0.41 mag, following the calibration by Munari and Zwitter (1997, A.Ap. 318, 269).