We report on high-energy femtosecond pulse generation from an ytterbium-doped rod-type fiber oscillator emitting around $976\mathrm{nm}$ . Self-starting and stable single-pulse operation are demonstrated with $4.2\mathrm{W}$ of average output power at a repetition rate of $8.4\mathrm{MHz}$ . The resulting energy level reaches $0.5\mathrm{\mu J}$ . Because of the all-normal dispersion of the laser cavity, output pulses are naturally chirped with a duration of $14\mathrm{ps}$ . External compression using diffraction gratings shortens the pulse duration down to $460\mathrm{fs}$ .