We have investigated the enhanced field emission at the contact between metal and dielectric. Such a strong enhancement of field emission has been often observed as a breakdown and is considered to be due to dielectric . It seems that the enhancement of emission has two reasons . One is the polarization of dielectric due to the charge on the metal. The polarization charges, in return, attract free charges on the metal toward the junction, which leads to the high surface chare density near the junction. The other is the space charges produced by the very enhanced field, in dielectric. Due to a lot of space charges, the contact barrier between metal and dielectric is thinned and lowered, which leads to the production of a detour path from metal through dielectric to vacuum. The detour path can be more preferable by the view of potential energy than the direct path from metal-vacuum. We evaluate the two effects to explain the enhancement of field emission in problem.