We describe about characteristics of creeping discharge developed in a narrow gap with a backside electrode, under μs pulse voltage application. As a result, in the gas with 3% SF6 mixture in N2, the flashover voltage in the pressures of 0.2 and 0.3MPa decreased by approximately 5% compared to that of 0.1MPa in both a filamentous straight backside electrode and a filamentous curve backside electrode. V-characteristics of which flashover voltage decreased were obtained by SF6 mixture in N2. We obtained V-characteristics on the flashover voltage at SF6 content in the range of D=3%-100% for a filamentous backside electrode. Flashover voltages at a filamentous straight backside electrode were higher than that of a filamentous curve backside electrode. From the corona observation using ultra-high speed camera, it was found that the flashover is generated along the backside electrode.