The synthetic amorphous silica powder of the present invention is characterized in that it comprises a synthetic amorphous silica powder obtained by applying a spheroidizing treatment to a silica powder, and by subsequently cleaning and drying it so that the synthetic amorphous silica powder has an average particle diameter D50 of 10 to 2,000 μm; wherein the synthetic amorphous silica powder has: a quotient of 1.00 to 1.35 obtained by dividing a BET specific surface area of the powder by a theoretical specific surface area calculated from the average particle diameter D50; a real density of 2.10 to 2.20 g/cm3; an intra-particulate porosity of 0 to 0.05; a circularity of 0.75 to 1.00; and a spheroidization ratio of 0.55 to 1.00.