To enable a viable count to be decreased without damaging the flavor and taste original to a powder.

This apparatus A for sterilizing the powder can kill live germs attaching to the powder by the sterilizing power of ozone gas by bringing the powder into contact with the ozone gas and mixing them in a step for milling buckwheat, wheat, rice, soybean or the like. The apparatus A for sterilizing the powder comprises an ozone gas-generating device 5, a blasting pump 2 for diluting the ozone gas to a prescribed concentration, a flow meter 4, an ozone gas concentration meter 1 for observing that the concentration of the diluted ozone gas is kept within the prescribed concentration range, and an ozone gas leak-detecting and alarming device 8 for detecting the ozone gas and giving the alarm when the ozone gas leaks from the ozone gas-generating device 5. The method for preserving the powder comprises carrying out the sterilizing treatment of the powder by the apparatus A for sterilizing the powder, and immediately bagging the sterilized powder after the sterilization. As a result, the ozone gas is shut into the bag, and the sterilization by the ozone gas is continued after the bagging.