We investigated long intrinsic Josephson junctions (IJJs) as an oscillator on a Bi2Sr2CaCu2O8+d (Bi-2212) whisker. The oscillator utilizes the effect of flux-flow motion in long IJJs. In-plane areas with the same junction geometry, 15×1.7 μm2 were fabricated by using a three-dimensional focused-ion-beam (FIB) etching method. Those oscillator junctions exhibited uniform multibranch structures and clearly upturned curves under He. The flux-flow velocities (Vff) reached 8.7×105 m/s at 6.2 T and 10 K. We describe the characteristic flux-flow behaviors on long IJJs for high-frequency device applications.