A pencil type ultrasonic probe to which a finger grip adapter is attached is fixed to a cable connected to an ultrasonic diagnosis apparatus. Operator's fingers are hooked on the adapter attached to the probe to allow the probe to be held by an operator's hand, thereby keeping the probe at a predetermined position of an organic body. The adapter comprises: a body having a through-hole in which the probe is inserted; and a finger grip portion extending from the body and allowing the operator's fingers to be hooked on. The body has a guide slit for allowing the cable to pass therethrough. Thus, the cable is guided into the through-hole through the guide slit, and the probe is inserted into the through-hole to be attached to the adapter. When the probe is pulled out from the through-hole of the body, the cable is located in the through-hole. Thereafter, the cable is taken out from the through-hole through the guide slit, so that the adapter can be quickly and easily detached from the cable.