A pneumatic baby-rivetting hammer has often raised the problem in the industrial health. An isolator made by an air-cushion was applied to the hammer, by which the idea of a low-pass filter was examined. The attenuation characteristic on this isolator observed on a vibration table was very well and quite simple, because a stable balance type was employed in mechanical structure of the isolator as compared with an isolator used in a rock-drill of leg-type (Part 2). The similar attenuation was also obtained from the practical test on the baby-rivetting hammer by using spectrum difference on the hammer without and with the isolator.