In order to examine the validity of Mott-Schottky model at organic/metal interfaces, the position of the vacuum level of N,N'-bis(3-methylphenyl)-N,N'-diphenyl -[1,1'-biphenyl]-4,4'-diamine (TPD) film formed on various metal substrates (Au, Cu, Ag, Mg and Ca) was measured as a function of the film-thickness by Kelvin probe method in ultrahigh vacuum (UHV). TPD is a typical hole-injecting material for organic electroluminescent devices. At all the interfaces, sharp shifts of the vacuum level were observed within 1 nm thickness. Further deposition of TPD up to 100 nm did not change the position of the vacuum level indicating no band bending at these interfaces. These findings clearly demonstrate the Fermi level alignment between metal and bulk TPD solid is not established within typical thickness of real devices.