Langmuir circulation is a large-scale secondary current in the cross-wind direction, associated with a generation of wind-induced water waves. This circulation is observed together with the high-speed and low-speed streaks, i.e., the convergence and divergence zones, respectively, generated in the wind direction. Mass and momentum are transferred from the divergence toward the convergence zone. Strong downflows are formed in the convergence zone. Such a circulation plays vital roles on three-dimensional mass and momentum exchanges; thus, it is very important to study hydrodynamic properties of Langmuir circulation in natural lakes and in the ocean. So, in the present study, PIV measurements were conducted in order to reveal the distributions of velocity vectors on horizontal planes and to consider the generation mechanism of Langmuir circulation.