Recently, active researches on tunnel magnetoresistance (TMR) are under progress with the objects of its technical applications such as magnetic sensors and magnetic random access memories. In spite of these studies, the understanding of the electronic states at the interfaces of the ferromagnetic tunnel junctions and of the effects of roughness on the tunnel conductance and TMR is not still complete. Quite recently, numerical results on the TMR in the first principles band calculations have been reported for junctions with clean interfaces. The calculated results show that the contribution of the states with certain wave vectors parallel to the interface becomes dominant, which are known as hot spots. We calculate the dependence of the tunnel conductance and TMR on the barrier thickness including the interface roughness, and show that the contribution of the hot spots to the tunnel conductance is reduced by the roughness. We further argue the possibility of appearance of interfacial state due to amorphous-like barrier structure and its effects on the TMR.