Scanning near-field optical microscopy facilitates the studies on optical properties of nanomaterials beyond the diffraction limit of light. It enables us to reveal the optical properties point by point on the nanomaterials. In this article, we review our recent works on optical properties and their spatial features of localized plasmons in noble metal nanoparticles, revealed by various near-field optical techniques. We show that photonic local density-of-states or optical fields on the nanoparticles are visualized by using near-field linear and non-linear spectroscopic imaging techniques. We also show that the plasmon wavefunction resonant with the incident field is visualized by the near-field methods. Finally, we present spatio-temporal behaviors of the nanoparticles upon the photoexcitation visualized by near-field time-resolved imaging technique. We analyze the origin of the characteristic transient images and discuss energy dissipation processes of the nanoparticles.