A method of molding a synthetic silica glass molded body by accommodating a synthetic silica glass block in a mold provided with a pressing portion, and by pressing the block while heating, the method comprising: a step of washing the synthetic silica glass block so that a concentration of copper which is present on the surface of the synthetic silica glass block is 2 ng/cm2 or less, and so that a concentration of aluminium thereon is 10 ng/cm2 or less, before accommodating the synthetic silica glass block in the mold; a step of heating high purity carbon powders in which a content of copper is 40 wt.ppb or less and a content of aluminium is 100 wt.ppb or less at a temperature condition of 1200° C. to 1900° C.; a step of heating the mold at a temperature condition of 1700° C. to 1900° C.; a step of applying the high purity carbon powders after the heating step on the inner surface of the mold after the heating step, before accommodating the synthetic silica glass block in the mold; and a step of molding the synthetic silica glass block in a predetermined form by pressing the block by means of the pressing portion while heating so as to the temperature of the block can be within a hold temperature range of 1500° C. to 1700° C., after accommodating the washed synthetic silica glass block in the mold.