The authors describe observations on the negative pulseless corona in air between plane and needle electrodes and reports the characteristics of the transition from the negative pulseless corona to spark breakdown by measuring the luminosity and the space potential of the discharge gap. For the measurement of the space potential, a triode tube electrometer was used. The luminosity near the plane electrode is strongest just before the spark breakdown, and the transition from negative pulseless corona to spark breakdown starts from the plane electrode. At the spark breakdown, the field intensity in this region is constant for gap length ranging from 8 to 16 mm. This field intensity is about 43 V cm-1 Torr-1. It is the condition of the transition from negative pulseless corona to spark breakdown that the relation alpha >or= eta is accomplished near the plane electrode.