Bone-Conduction threshold is essential in pure tone audiometry together airconduction threshold for distinguishment whether hearing loss is conductive, sensorineural or mixed type and bone-conduction vibrator placement is also important for obtaining more accurate threshold. The bone-conduction threshold was obtained at the forehead, mastoid tip and mastoid upper portion with 50 persons (100 ears) of normal listeners for evaluation of the advantage at the three locations using the Nagashima 51A-T72 audiometer (ref=ISO). Author conclude the result as follows. 1) Bone-conduction threshold of the forehead was 5.5~4.7 dB, -8.1~8.3 dB at the mastoid tip and -9.1~8.7 dB at the mastoid upper portion and the thresholds of the middle and high tone frequencies were higher than the lower frequency. 2) Test-retest difference were 4.7~7.6 dB at the forehead, 5.5~7.0 dB at mastoid tip and 5.0~6.8 dB at mastoid upper portion, and there was no significant difference in three locations. 3) The difference between the mean thresholds of the mastoid tip and the mastoid upper portion was meaningless but the difference between the forehead and the mastoid tip was about -2.1~15.0 dB. And the largest average differences were found in the lower frequencies at 250 Hz and 500 Hz (13.6~15.0 dB) and the smallest difference was observed at 4,000 Hz (-2.1 dB). 4) Author suggest that the mastoid bone conduction test is more reasonable than the forehead, because the former is easier in masking and its threshold is more accurate than the latter.