This paper describes a prototype mechanical white noise generator has a source level of more than 170.0 dB (re 1µPa at 1 m) at the frequency range of 10 Hz to 100 kHz. The results of performance evaluation of the generator are as follows. The average source level of the generator measured by a step of 15°in horizontal (0 to 360。, 25 points) was 185.2 (SD (standard deviation): 2.3) dB (re 1µPa at 1 m). The maximum and minimum source levels were appeared at the frequency range of 2.5 to 5.0 kHz and around 100 kHz, respectively. The average source levels at 0°, 90。, 180。and 270° were 162.9 (SD: 10.6), 168.4 (SD: 10.0), 162.1 (SD: 9.1) and 166.5 (SD: 11.1) dB (re 1µPa at 1 m). The average source level measured by a step of 30° in vertical was 184.9 (SD: 2.2) dB (re 1µPa at 1 m). The relative maximum variation width of the source levels in horizontal and in vertical measurement were less than 7.0 dB and 1.0 dB, respectively.