need to select the optimal broad-band filters for the fitting so as to avoid strong spectral features. In the rest-frame UV and optical wavelength range, the redshifted Ly$\alpha$ ($\lambda$ $=$ 1216Å) line (or Lyman break) and Balmer break ($\lambda$ $\sim$ 3600Å) can be a contamination affecting the broad-band photometry. Figure \[fig4\] illustrates the position of the Lyman and Balmer breaks in the observed-frame, and filter profiles of the optical and NIR broad-band. For the sake of clarity, we show three model spectra with clear Lyman and Balmer breaks at *z* $=$ 3, 4, and 5, and we omit the filter profiles of Subaru/updated-*z’*, HST/F125W, F160W, Spitzer/3.6$\>\micron$, and 4.5$\>\micron$ bands. This figure indicates that the *R* ($\lambda$ $\sim$ 6000–7000Å) and *H* ($\lambda$ $\sim$ 15000-17000Å) band filters are probably affected by Lyman or Blamer breaks, and the wavelength coverage from *i’* to *J* band (black horizontal line in upper panel of figure \[fig4\]) is suitable for calculating the UV slope $\beta$ value of *z* $\sim$ 4 LBGs. Consequently, we use the Subaru/*i’*, *z’*, updated-*z’*, UKIRT/*J*, and HST/F125W band filters.

Another critical point is that the robustness of the $\beta$ measurement for the faint and blue galaxies is strongly influenced by the depth 