A reactor for nanoparticle production comprising a main chamber including a first nozzle to which raw material gas is supplied, a lens housing connected to the main chamber in a fluidly movable manner and including a second nozzle for supplying flushing gas to the lens housing, a lens mounted on the lens housing, a light source for irradiating a laser, which passes through the lens to reach the raw material gas in the main chamber, and a hood for discharging nanoparticles generated in the main chamber. A cross-sectional area of at least a part of the lens housing decreases along a direction facing the main chamber.