The effects of water current on the development of wind waves are investigated experimentally. When the direction of current is opposite to that of a wind, wave length and height of wind waves become greater than that of wind waves without current. In the case of a fabvourable current, the situation is opposite. From the engineering point of view, therefore, the investigation of the development of wind waves in adverse current is more important than that in favourable current.
　Experiments were performed in a wind-wave tank. Waves were measured with resistance-type wave gages at seven stations. The velocity of the current was measured with a laser-Doppler anemometry.
　The following conclusions are drawn from the present study.
(1) In a strong adverse current, generated wind waves are likely to form a wave group. The propagation velocity of the wave group is nearly equal to the group velocity.
(2) A new formula for the development of significant wave height in adverse current is proposed.