We report a regenerative amplifier based on an Yb-doped apatite crystal: Yb3+:SrY4(SiO4)3O (Yb:SYS). We obtained 420-fs pulses at a central wavelength of 1066 nm with an energy of 100 microJ at 300 Hz after compression. To the best of our knowledge, this system is the first regenerative amplifier based on an Yb:SYS crystal and provides duration among the shortest ones generated by a directly diode-pumped regenerative amplifier.