  We present results from a narrow-band optical survey of a contiguous area of
1.95 deg^2, covered by the Cosmic Evolution Survey (COSMOS). Both optical
narrow-band (lambda_c = 8150 AA and Delta_lambda = 120 AA) and broad-band (B,
V, g', r', i', and z') imaging observations were performed with the Subaru
prime-focus camera, Suprime-Cam on the Subaru Telescope. We provide the largest
contiguous narrow-band survey, targetting Ly alpha emitters (LAEs) at z~5.7. We
find a total of 119 LAE candidates at z~5.7. Over the wide-area covered by this
survey, we find no strong evidence for large scale clustering of LAEs. We
estimate a star formation rate (SFR) density of ~7*10^-4 M_sun yr^-1 Mpc^-3 for
LAEs at z~5.7, and compare it with previous measurements.
