Phosphate optical glass having an Abbé number, νd, of greater than 59. A preform for precision press molding being comprised of the phosphate optical glass. An optical glass being comprised of the phosphate optical glass and manufacturing method of the same. Provided are low-dispersion phosphate optical glass having a low-temperature softening property and good weatherability, suited to precision press molding, and further having good devitrification stability, a preform for precision press molding comprised of the above glass and a method of manufacturing of the same, a glass optical element having the above optical characteristics as well as good weatherability and a method of manufacturing the same.