This paper reports a newly developed pneumatic pressure wave generator. The developed pressure wave generator responds to the requirement of the dynamic calibration of pressure sensors that must detect small differential pressures. A closed chamber of about 200 milliliters capacity is filled with air and stuffed with a thin metal wire bundle. A small piton is inserted into the cabinet. When the piston moves, the pressure in the chamber changes correspondingly. The stuffed wire bundle has a large heat capacity which absorbs generated heat by air compression of air. Consequently, the air temperature in the chamber is kept almost constant; hence the pressure amplitude becomes almost independent from the change of frequency of the piston motion. Experiments are performed with various volume of stuffed wire, whose range is from zero to ten percent of the box space, and with various frequencies of piston motion. This paper gives a theoretical base of the characteristic of the wave generator, which is verified by experiments. Obtained experimental results satisfied the requirement of the constancy of the pressure amplitude and negligible phase lag for intended range of frequency, i.e., one to fifty Hz . The experimental results also proved that the selected parameters can respond to the design purpose of the pressure wave generator.