The wave generators which have been used so far, such as flap-type-generator etc., have an inconvenience that the waves reflected by a model structure are reflected again by the wave paddle and disturb the incident waves. In this note,the design of a wave generator of verticaly oscillating flow type which is capable of removing the above inconvenience is discussed with the results of its characteristic tests.
　The wave generator was attached to a wind wave channel of 60 cm wide and 22 m long. The wave paddle is a level rectangular plate moving up and down in a vertical hole (588×400mm) opened at the channel bottom. The period of generated waves is 0.6～6.6sec, the wave height is 10～12cm at the maximum and the reflection coefficient is 7～8 percent on the average; the wave reflection at the wave maker is very small. Hence the wave profiles recorded for several minutes show little variation both in profiles and wave heights with lapse of time. The generated wave heights are in good agreement with the theoretical values given by Goda except those near the points of wave breaking. The appearance limit of the secondary wave crests are almostthe same with that of flap-type-generator.