Influence of the defects in the diamond films on electron emission has been studied by using electron spin resonance (ESR) method. The defect density in the diamond film increased up to a order of 10(18) spins/cm(3) when the CH, concentration was increased at 5 %. When the defect density in the diamond film is sufficiently high, electrons are efficiently supplied to the diamond surface from the back of the diamond film through defect-induced energy band by a hopping conduction. Therefore, the emission current at the applied electric field of 8 V/mum increased up to 1x10(2) muA/cm(2) with increasing the defect density.