The field-effect transistor fabricated with N,N'-bis(3-methylphenyl)-N,N'-diphenyl- 1,1'-biphenyl-4,4'-diamine (TPD) on a silicon substrate has shown a p-channel organic field-effect transistor (OFET) operating in the accumulation mode. The hole mobility in the TPD layer has been obtained to be 7.2 x 10(-4) cm(2) V-1 s(-1). Gate-voltage-induced infrared absorption from the OFET has been measured in the transmission-absorption configuration by the FT-IR difference-spectrum method. The observed spectra depend on the gate voltage applied. The vibrational Stark effect and the bands originating from the carriers injected into the TPD layer have been observed.