The present invention relates to an optical glass which has a low glass transition temperature (Tg) and optical constants in which a refractive index (nd) is in the range of from 1.70 to less than 1.74 and an Abbe number (nud) is between 40 and 45 (excluding 40 and 45), has a content of SiO2 is 17% by mass or less, a glass transition temperature (Tg) is 540 DEG C or less, and a weathering resistance (surface-method) in Class 1 or 2, and has excellent chemical durability, particularly weathering resistance (surface-method) and is appropriate for precision mold press forming.