This paper describes results of 3-D imaging of a fault in Nakatatsu mine, Japan, with the directional borehole radar. The receiving antenna in the radar is the coaxial-fed circular dipole array antenna. The array data are acquired in singlehole measurement with the antenna. We propose a method to construct 3-D images of a plane type reflector from the array data. A numerical example is given to verify the method. In this simulation, we generated the array data with the MoM modified for borehole radar. The field experiments were conducted to measure a fault in skarn with the directional borehole radar. We detected reflected waves from the faults, and constructed 3-D images of the fault.