An instrument location determining device which has a radiating element forming part of the instrument to be inserted into an object. The element radiates a signal and the signal is detected by at least one receiving element. A signal energy level measurement device is coupled to the receiving element and it produces an energy level value for each one of the receiving elements. The distance of the radiating elements from the receiving element is calculated from the measured energy level values received by each of the receiving elements. The measured distance is then indicated to an operator of the instrument so that he can locate the instrument within the object.