Silver clusters, consisting of several to tens of Ag atoms, are known to be modeled by a three-dimensional quantum well, where free electrons originating from valence Ag 5s are confined. Since the quantum well forms discrete energy levels denoted as 1S, 1P, 1D, 2S, etc., the free electrons are accommodated in these so-called superatomic orbitals in accordance with the number of electrons contributing to orbital filling. Here we demonstrate by our photoelectron-imaging experiment that such orbitals are indeed formed. For example, 1S21P61D102S1 configuration with 19 valence electrons would be realized for the anionic Ag18- cluster. Its photoelectron image exhibits an angular anisotropy characteristic of detachment from an S-type orbital, providing us with a firm evidence for the 2S character of the outermost orbital [1]. A similar anisotropy is observed for Ag15Sc-, which is shown to be an analogue of Ag18- with contributions of three electrons from Sc 3d14s2 [2]. We also examine closed-shell clusters with 1S21P61D10 configuration as well as other species in a broad size range. Furthermore, photoabsorption spectroscopy will be presented to discuss plasmonic behaviors of silver clusters [3].