The present invention relates to an exposure apparatus using a projection optical system to realize a small size and the bitelecentricity as securing a wide exposure area and a large numerical aperture and to realize extremely good correction for aberrations, particularly for distortion. The projection optical system comprises a first lens group G.sub.1 with a positive refracting power, a second lens group G.sub.2 with a negative refracting power, a third lens group G.sub.3 with a positive refracting power, a fourth lens group G.sub.4 with a negative refracting power, a fifth lens group G.sub.5 with a positive refracting power, and a sixth lens group G.sub.6 with a positive refracting power in order from the side of the first object R, wherein the second lens group G.sub.2 comprises a front lens L.sub.2F with a negative refracting power, a rear lens L.sub.2R of a negative meniscus shape, and an intermediate lens group G.sub.2M disposed between the front lens and the rear lens, and wherein the intermediate lens group G.sub.2M has a first lens L.sub.M1 with a positive refracting power, a second lens L.sub.M2 with a negative refracting power, and a third lens L.sub.M3 with a negative refracting power in order from the side of the first object R. The system is arranged to satisfy within suitable ranges of focal lengths for the first to sixth lens groups G.sub.1 -G.sub.6, based on the above arrangement.