The ε-iron oxide powder has an average particle size in a range of 5.0 to 16.0 nm and an uneven distribution of an M atom in a surface layer portion, in which the M atom is one or more kinds of atoms selected from the group consisting of an aluminum atom and an yttrium atom, and a content of the M atom with respect to 100 atom % of iron atoms is in a range of 4.0 to 9.5 atom %.