Photometric properties of Ly emitters at z = 4.86in the COSMOS 2 square degree field()()()()COSMOS We present results of a survey for Ly emitters at z =4.86 based on optical narrowband (C=7126 , =73) andbroadband (B, V, , i, and z) observations of the Cosmic Evolution Survey (COSMOS) field using Suprime-Cam on the Subaru Telescope. We find 79 LAE candidates at z=4.86 over a contiguous survey area of 1.83 deg2, down to the Ly line flux of 1.47x 10-17 ergs s-1 cm-2. We obtain the Ly luminosity function with a best-fit Schechter parameters of log L*=42.9+0.5-0.3 ergs s-1 and * = 1.2+8.0-1.1 x 10-4 Mpc-3 for =-1.5 (fixed). The two-point correlation function for our LAE sample is (r) = (r/4.4+5.7-2.9Mpc)-1.900.22. In order to investigate the field-to-field variations of the properties of Ly emitters, we divide the survey area into nine tiles of 0.5 deg x 0.5 deg each. We find that the number density varies with a factor of 2 from field to field with high statistical significance. However, we find no significant field-to-field variance when we divide the field into four tiles with 0.7 deg x 0.7 deg each. We conclude that at least 0.5 deg2 survey area is required to derive averaged properties of LAEs at z 5, and our survey field is wide enough to overcome the cosmic variance. ABSTRACT2.LyResultsSampleLy Blue lines: Coleman, Wu, Weedman(1980), Green lines: Kinney et al. (1996)s starburst, Red line: Bruzual & Charlot (2003)ssynthesized SED with emission lines.B-dropout79 LAEsMUV=-21.5 LAEs 20.5deg x 0.5deg field-to-field variations 20.7 deg x 0.7 deg 0.5deg x 0.5deg 0.7deg x 0.7deg Correlation lengthMpc 3 < z < 6 3 < z < 6 UVLF MUV=-21.5 Ouchi et al. (2008) z=4.9 z=3.1-3.7 z=5.7