Ge surfaces were irradiated by Ar+ ions at 600 eV with and without a simultaneous supply of Ge, Au or Al at room temperature. The surfaces ion-irradiated without any simultaneous metal supply were characterized by densely distributed conical protrusions. By contrast, various kinds of nanostructures were formed on the Ge surfaces ion-irradiated with a simultaneous metal supply. They featured cones and nanobelts with a flattened top for Ge supply cases, whereas they were characterized by nanorods for Au supply cases and by nanorods, nanobelts and nanowalls for Al supply cases. Very interestingly, the nanorods formed with Au or Al supply possessed a bottleneck structure. Thus, the ion-induced Ge nanostructures were controllable in morphology by species and amount of simultaneously supplied metals.