We produced niobium clusters over a wide size range(Nb-n: 1 less than or equal to n less than or equal to 1000) by a laser ablation method in a low-pressure condensation source. Mass spectra of the neutral clusters, positive and negative ion clusters were measured by a time-of-flight mass spectrometer with a high mass resolution and a wide mass range. Similarity and difference in their mass spectra were examined to understand the cluster generation process in different charged states.