A carrier core material for an electrophotographic developer containing Li ferrite, maghemite, and Fe3O4, wherein a part thereof is substituted with Mn, a Li content is 1 to 2.5% by weight, a Mn content is 2 to 7.5% by weight, and a silicon content is 25 to 10,000 ppm, a compression breaking strength is 130 MPa or more, an SF-1 is 125 to 145, respective cumulative strengths of respective spinel crystal structure faces in X-ray diffraction satisfy a certain equation, a vacuum resistivity R500 across a 2 mm gap when a measurement voltage of 500 V is applied is 1×106 to 5×109 Ω, and a vacuum resistivity R1000 across a 6.5 mm gap when a measurement voltage of 1,000 V is applied is 5×107 to 1×1010 Ω.