[en] LaO${}_{0.5}$F${}_{0.5}$BiSe₂ is a new layered superconductor discovered recently, which shows the superconducting transition temperature of 3.5 K. With angle-resolved photoemission spectroscopy, we study the electronic structure of LaO${}_{0.5}$F${}_{0.5}$BiSe₂ comprehensively. Two electron-like bands are located around the $X$ point of the Brillouin zone, and the outer pockets connect with each other and form large Fermi surface around $\mathrm{\Gamma <!--\; ??\; -->}$ and $M$. These bands show negligible $k_z$ dispersion, indicating their two-dimensional nature. Based on the Luttinger theorem, the carrier concentration is about 0.53 e${}^{-<!--\; ???\; -->}$ per unit cell, close to its nominal value. Moreover, the photoemission data and the band structure calculations agree very well, and the renormalization factor is nearly 1.0, indicating the electron correlations in this material are rather weak. Our results suggest that LaO${}_{0.5}$F${}_{0.5}$BiSe₂ is a conventional BCS superconductor without strong electron correlations. (paper)