Two kinds of NiO films with different crystallinity were fabricated by controlling the film deposition conditions. The well-crystalline film showed resistive switching characteristics whereas the poorly-crystalline film did not. From I-V characteristics of the NiO bilayer film consisting of those two kinds of films, it was found that the initial characteristics significantly differed according to the bias polarity. The forming voltage became lower and had less variety when the well-crystalline side was positively-biased. These results suggest that the forming voltage and currents are controllable by modifying the film properties at the metal-oxide interfaces.