A digital hearing aid enhancing a directional performance for a patient who suffers from sole-ear hearing impairments is provided, in which the digital hearing aid cell inserted into one healthy ear is electrically connected with another digital hearing aid cell called an ear cell including a microphone worn in the other troubled ear, via an external electric wire. Two digital hearing aid cells are connected with each other via signal, power, and ground wires to thereby adjust a time delay parameter and thus make a time delay effect between the two microphones, so that a wearer who wears the digital hearing aid can better hear sound which comes from the side opposing the healthy ear, that is, from the troubled ear side.