A silicon oxide powder can be continuously prepared by feeding a raw material powder mixture containing silicon dioxide powder into a reaction chamber (2) at a temperature of 1,100-1,600.degree. C., to produce a silicon oxide gas, transferring the silicon oxide gas to a deposition chamber (11) through a transfer conduit (10) maintained at a temperature of from higher than 1,000.degree. C. to 1,300.degree. C., causing silicon oxide to deposit on a substrate (13) which is disposed and cooled in the deposition chamber, scraping the silicon oxide deposit, and recovering the deposit in a recovery chamber (18). The method and apparatus is capable of continuous and stable production of amorphous silicon oxide powder of high purity.