We propose a bad-cavity laser based on the Raman transition of cesium-133 atoms that collectively emit photons into the wide mode of a low finesse resonator, which is known as the optical bad-cavity regime. The spinspin correlation, which characterizes the collective effect, is demonstrated. We theoretically predict that the optical radiation has an extremely narrow linewidth in the 98×10^-2 mHz range, and that a power level of 7×10^-10 W is possible.