Provided herein is a soft magnetic alloy powder that can exhibit a high saturation flux density and desirable soft magnetic characteristics. A dust core using such a soft magnetic alloy powder is also provided. A soft magnetic alloy powder is used that includes an amorphous phase, and an αFe crystalline phase residing in the amorphous phase. The αFe crystalline phase has a crystallite volume distribution with a mode of 1 nm or more and 15 nm or less, and with a half width of 3 nm or more and 50 nm or less.